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THE FUNDAMENTALS 

OF 

FRUIT PRODUCTION 



BY 

VICTOR RAY GARDNER 
FREDERICK CHARLES BRADFORD 

AND 

HENRY DAGGETT HOOKER, JR. 

OP THE DEPARTMENT OF HORTICULTURE OP THE UNIVERSITY OF MISSOURI 



First Edition 



McGRAW-HILL BOOK COMPANY, Inc. 
NEW YORK: 370 SEVENTH AVENUE 

LONDON: 6 & 8 BOUVERIE ST., E. C. 4 

1922 









S3^ 5 

.&3- 



Copyright, 1922, by the 
McGraw-Hill Book Company, Inc. 






* THE HiPLl PRESS T O R K P. 



APR 18 1922 
§)C!.A661347 



PREFACE 

Fruit growing in the United States is so widespread and so diversified 
that no work of ordinary dimensions can codify it on the basis of empirical 
practices, which differ from place to place. The fundamental factors, 
however, are always the same and once they are understood, the adapta- 
tion of practices to local conditions presents little difficulty. 

The present work attempts to focus attention on the conditions 
which make the fruit plant profitable; practices are considered only as 
they affect these conditions, not as ends in themselves. Maintenance 
of this point of view has necessitated a rather wide departure from con- 
ventional arrangement of subject matter. The common orchard prac- 
tices are not sacred in themselves; indeed, they are important only in so 
far as they help vegetative growth and especially fruit production. 
Fundamentally the plant's growth and functioning depend on the nature 
of the environment and the adjustment thereto and not directly on cul- 
tural practices, which only modify the relation of the plant to the environ- 
mental complex. Consequently these practices appear inconspicuous in 
the Chapter and Section headings. 

Acquaintance with principles without the facts on which they rest 
is itself empirical. Particular attention, therefore, is given to the 
inclusion of sufficient illustrative matter to permit quantitative estimate 
of the validity and applicability of the principles enunciated. Com- 
paratively little that is original is presented; much of the material that is 
novel to pomological texts is included because of its inaccessibility to the 
average student. Many significant observations which have been neg- 
lected because their ultimate bearing was not appreciated at the time 
they were recorded, have been reviewed in the light of modern knowledge. 
Plant physiology, plant chemistry, soil science and physics have been 
requisitioned freely and advisedly; in no case, however, without an indi- 
cation of applicability to pomology. Careful consideration has approved 
this course because special applications to fruit growing are rare in the 
general University courses in these subjects and because in the arrange- 
ment of many curricula, pomology precedes some of the science courses 
which are needed as preparatory training. Though every effort is made 
to insure thoroughness, exhaustiye treatment is not attempted, since it 
would be useful to few readers. 

The solution of a problem arising outside of the classroom depends on 
obtaining all the pertinent data, systematizing them to ascertain the 
factors involved and applying to the problem th.e knowledge so gained. 



vi PREFACE 

This text is designed to prepare the student to undertake these steps. 
As with any text, much is necessarily left to the instructor, particularly 
matters of opinion and of local application. 

Finally, it hardly need be said that this text is intended for students 
of college grade. It is not a manual on how to grow fruit; it does not 
attempt to enter fields best covered by classroom discussion, laboratory 
work or practical experience. It is intended, however, to be a supple- 
ment and guide to these. 

The writers wish to express their appreciation of the helpful criticisms 
and suggestions offered by those to whom portions of this manuscript 
have been submitted: to Dr. M. M. McCool of the Michigan Agricultural 
Experiment Station (the Section on Water Relations); to Dr. William 
Crocker of the University of Chicago and to Dr. E. J. Kraus of the 
University of Wisconsin (the Section on Nutrition) ; to Dr. W. H. Chand- 
ler of Cornell University (Chapters 14-18, dealing with Winter Injury) ; 
to Dr. 0. M. Stewart, Professor of Physics in the University of Missouri 
and to George Reeder of the U. S. Weather Bureau (Chapters 19 and 20 
on Frost Occurrence and Control) ; to Prof. Ray Roberts of the University 
of Wisconsin (the Section on Pruning) ; to Dr. M. J. Dorsey of the Uni- 
versity of Minnesota (the Section on Fruit Setting) ; to Prof. W. P. Tufts 
of the University of California, to Dr. J. K. Shaw of the Massachusetts 
Agricultural Experiment Station and to Paul C. Stark of the Stark Bros. 
Nursery Co. (the Section on Propagation) ; to Prof. Roy E. Marshall of 
the Michigan Agricultural College and to Prof. W. P. Tufts of the Uni- 
versity of California (Chapters 34 and 35 on Orchard Locations and 
Soils); finally to Dr. C. V. Piper. Many valuable criticisms and sug- 
gestions have been incorporated in the text. In a few instances the 
writers have believed themselves justified in adhering to their original 
interpretations of the evidence, so that these authorities who have 
assisted the writers very materially are not to be held responsible for 
any part of the book in its present form. 

Acknowledgment is made also to Prof. C. E. Shuster of the Oregon 

Agricultural Experiment Station for Figures and to Dr. J. K. Shaw of the 

Massachusetts Agricultural Experiment Station for Figure 56. 

Columbia, Mo. The AUTHORS. 

August, 1921. 



CONTENTS 

Page 

Preface v 

SECTION I 

Water Relations 

CHAPTER I 

The Water Requirements of Fruit Plants 3 

Water as a Plant Constituent — The Water Requirements of Plants in Terms 
of Dry Weight — The Water Requirements of Plants in Terms of Precipita- 
tion — Amounts Used by the Plants Themselves; Total Amounts Required 
for Plants and to Compensate for Evaporation, Runoff and Seepage — Plant- 
ing Distances Related to Moisture Supply — Factors Influencing the Water 
Requirements of Plants — Nutrient Supply; Cultivation; Light; in General; 
Some Applications to Practice — The Wilting Point for Fruit Plants — Wilting 
Coefficients; Wilting under Field Conditions; Wilting Coefficients and 
Drought Resistance — Summary. 

CHAPTER II 

The Intake and Utilization of Water 18 

Water Absorption — The Water Absorbing Organs — The Handling and 
Transplanting of Nursery Stock — The Water Absorbing Process — Factors 
Enabling the Roots to Exploit the Soil; Adaptation of Roots to Moisture 
Conditions; Factors Influencing Rate of Absorption; Submergence and Root 
Killing— Transpiration — Cuticular and Stomatal Transpiration Compared; 
Variability in Number of Stomata in Accordance with External Conditions — 
Factors Influencing Rate of Transpiration — Character of Cuticle; Age of 
Leaf; Defoliation, Summer Pruning; Wind Velocity, Windbreaks; Light; 
Temperature, Slope of Ground — The Water Conducting System of the Tree 
— Summary. 

CHAPTER III 

Orchard Soil Management Methods and Moisture Conservation ... 31 
Orchard Soil Management Methods Defined and Described — Orchard Soil 
Management Methods and Surface Run-off — Moisture Under Tillage and 
Sod-Mulch Systems of Management — Some New York and Pennsylvania 
Records; Some New Hampshire Records; English Experience; Some 
Kentucky and Kansas Records; in General; Practicability of Sod-mulch 
System Influenced by Depth of Rooting — Influence of Depth and Frequency 
of Cultivation upon Soil Moisture — Intercrops and the Soil Moisture Supply 
— Cover Crops and the Moisture Supply — Effects of Early and Late Seeding; 
Winter-killed and Winter-surviving Cover Crops — Wind Velocity and 
Evaporation, Windbreaks — Summary. 

vii 



viii CONTENTS 

CHAPTER IV 

Page 

Soil Moisture: Its Classification, Movement and Influence on Root 

Distribution 47 

Classification of the Water in Soils and Plant Tissues — The Response of 
Water to the Force of Gravity and the Evaporating Power of the Air; 
the Relative Saturation; Resistance to Freezing — Movement of Water in the 
Soil — Percolation; the Rise of Water by Capillarity; Lateral Movement of 
Water in the Soil — The Distribution of Fruit Tree Roots as Influenced by Soil 
Moisture — The Idea 1 Root System — Specific and Varietal Differences in Root 
Distribution — The Distribution of Tree Roots under Varying Conditions — 
In the Hood River Valley, Oregon and in Ohio; in a Gravelly Loam, Underlaid 
by Hardpan, in Maine; in a Thin Gravelly Loam, Underlaid by Rock, in 
Maine; in Dwarfs; the Influence of Soil Moisture; the Influence of Culti- 
vation; the Influence of Soil "Alkali" — Applications to Orchard Practice — 
Summary. 

CHAPTER V 

The Response of Fruit Plants to Varying Conditions of Soil Moisture 

and Humidity 66 

Influence of Soil Moisture on Vegetative Growth — New Shoots and their 
Leaves; Annual Rings and Trunk Circumference; Moisture Supply and the 
Growth Period in Early Spring; the "Second Growth" of Midsummer or Late 
Summer — Influence of Water Supply on the Development of Fruit — Size; 
Yield; Shape and Color; Composition; Disease Resistance and Susceptibility 
— Residual Effects of Soil Moisture — On Vegetative Growth; on Yields — 
Influence of Atmospheric Moisture on Growth— In General; Russeting of 
Fruit; Fruit Setting — Summary. 

CHAPTER VI 

Pathological Conditions Associated with Excesses and Deficiencies in 

Moisture 83 

Disturbances Due to Moisture Excesses — The Splitting of Fruit; (Edema; 
Fasciation and Phyllody; Chlorosis; Rough Bark or Scaly Bark Disease; 
Watercore — Disturbances Due to Moisture Deficiencies — Defoliation, 
Premature Ripening of Wood — Dieback — Cork, Drought Spot and Related 
Diseases — Fruit-pit; Cork; Surface Drought Spot; Deep-seated Drought 
Spot; Dieback and Rosette; Bitter-pit; Jonathan-spot; Black-end — Silver 
Leaf — Lithiasis — Summary. 

SECTION II 
Nutrition 

CHAPTER VII 

Plant Nutrients and Their Absorption 101 

Distribution of Elements Found in Ash — In Tissues of Different Kinds; in 
Tissues of Different Age; at Different Seasons — Absorption — The Osmotic 
System — Displacement — Availability of Ash Constituents — Availability 
and Solubility Distinguished; Factors Influencing Solubility; Availability of 



CONTENTS IX 

Page 
Phosphorus; Availability Varies According to Kind of Plant; Availability of 
Iron and Sulfur — Availability of Nitrogen — Nitrification — Aided by Liming; 
Influenced by Methods of Soil Management; Influenced by Temperature and 
Soil Moisture — Losses of Nitrogen from the Soil — Maintaining the Nitrogen 
Supply of the Soil — Nitrogen Fixation — Soil Reaction, Acidity and 
Alkalinity — Soil Reaction and the Availability of Phosphorus; Soil Reaction 
and the Availability Of Iron; Acid Tolerance of Certain Crops — Concent- 
ration, Soil "Alkali" — Tolerance of Different Fruits; Injuries from Excessive 
Fertilization; some effects of Soil Alkali; Remedial Measures — Soil Toxicity 
— General and Specific Effects; Protecting Against Toxins; Importance in 
the Fruit Plantation — Antagonism; Aeration; Selective Absorption — 
Transpiration — The Nutrient Requirements of Crop and Fruit Plants — 
Summary. 

CHAPTER VIII 

Individual Elements 130 

Nitrogen — Synthesis of Organic Nitrogenous Compounds — Translocation 
and Use of Elaborated Nitrogenous Compounds — Seasonal Distribution of 
Nitrogen — In Leaves; in Branches, Trunks and Roots; in Spurs; in Fruit; in 
Various Tissues of Trees of Different Age — Phosphorus — Synthesis of Phos- 
phorus-contain : ng Organic Compounds — Translocation and Use of Phos- 
phorous-containing Compounds — Amounts Used in Fruit Production — 
Seasonal Distribution of Phosphorus — In Leaves; in Branches, Trunk and 
Roots; in Spurs; in Fruit; in Various Tissues of Trees of Different Ages — Potas- 
sium — Synthesis, Translocation and use of Potassium-containing Compounds 
— The Demand and the Supply — Seasonal Distribution of Potassium — 
In Leaves; in Branches, Roots and Trunks; in Spurs; in Fruit; in Various Tis- 
sues of Trees of Different Age — Sulfur — Iron — Magnesium — Calcium — 
Seasonal Distribution of Calcium — In Buds and Leaves; in Bark and Wood; 
In Fruits — The Demand and the Supply — Other Mineral Elements — Silicon; 
Sodium; Chlorine; Aluminum and Manganese — Summary. 

CHAPTER IX 

Manufacture and Utilization of Carbohydrates 161 

Assimilation and Limiting Factors Defined — Carbon Assimilation — Factors 
Involved — Carbon Dioxide; Water; Light — Leaf Pigments — Variation with 
Age; Variation with Light Supply — Temperature; Enzymes — Products 
— Oxygen — Carbohydrates — Daily and Seasonal Fluctuation in Leaves; 
Forms of Storage — Seasonal Fluctuations of Stored Carbohydrates — Easily 
Hydrolizable Carbohydrates; Starch; Sugars — Carbohydrate Utilization — . 
In Tissue Building; in Retaining Moisture; Increasing Osmotic Concentra- 
tion; as a Source of Energy; Relation to Pigment Formation — Summary. 

CHAPTER X 

The Initiation of the Reproductive Processes 181 

The Development of the Fruitful Condition — The Response of the Plant 
to Changes in Relative Amounts of Nitrogen and of Carbohydrates — The 
Significance of Carbohydrate Accumulation, Manufacture in Excess of 
Utilization — In Fruit Spurs; Influence of the Nitrate Supply; Influence of the 
Moisture Supp'y; Influence of Other Factors — Fruit-bud Formation — 



x CONTENTS 

Page 
Evidence of Differentiation — Time of Differentiation — In Relation to Posi- 
tion; Varietal Differences; Differences Induced by Cultural Treatment — 
Abnormalities; Winter Stages — Summary. 

CHAPTER XI 

Surpluses and Deficiencies 194 

Surpluses— Nitrogen; Magnesium; Copper; Arsenic; Manganese; Other 
Elements — Deficiencies — Nitrogen; Phosphorus and Potassium; Sulfur; 
Iron; Magnesium and Calcium; Chlorine — Analysis of the Fertilizer Problem 
— The Fertilizer Requirements of the Orchard. 

CHAPTER XII 

The Application of Nitrogen-carrying Fertilizers 204 

The Influence of Nitrogenous Fertilizers on Vegetative Growth — In Peaches; 
in Apples; in Strawberries; Negative Results, Nitrogen not a Limiting 
Factor — Influence of Nitrogen on Blossom-bud Formation — in Peaches; in 
Apples — Influence of Nitrogen on the Setting of Fruit — Influence of Nitro- 
gen on Size of Fruit — Influence of Nitrogen on Color of Fruit — Influence of 
Nitrogen on Yield — The Correlation Between Vegetative Growth and 
Yield — Influence of Nitrogen on Composition and on Season of Maturity — 
Summary. 

CHAPTER XIII 

Fertilizers, Other Than Nitrogenous, in the Orchard 218 

The Indirect Effects of Fertilizers — Phosphoric Acid; Sulfur; Lime — 
Plant Nutrient Carriers, Different Forms of Fertilizers — Nitrogen from 
Inorganic Sources; Nitrogen from Organic Sources; Phosphorus; Potassium; 
Sulfur; Lime— Season for Applying Fertilizers — The Relations of Seasonal 
Conditions to Response From Fertilizers — Summary. 



SECTION III 
Temperature Relations of Fruit Plants 

CHAPTER XIV 

Growing Season Temperatures 236 

Heat Units — The Relative Values of Different Effective Temperatures — 
Influence of Latitude on Heat Requirements — In the Early Harvest Apple; 
in the Elberta Peach; in Chestnut Blight — Variations in Heat Requirements 
from Season to Season — Acclimatization to Varying Amounts of Heat — In 
General — Optimum Temperatures — Variation within the Species or Variety; 
Differences within the Variety for Separate Processes; Variation in Quality 
with Amount of Summer Heat; Variation in Season of Maturity with 
Amount of Summer Heat — Soil Temperatures — Indirect Temperature 
Effects — Summary. 



CONTENTS xi 

CHAPTER XV 

Page 

Winter Killing and Hardiness 250 

Death from Freezing — Tissue Freezing is Accompanied by Cell Dehydration; 
Freezing, Not Cold, Kills; Freezing and the Deciduous Habit — Increasing 
Hardiness — By Increasing Sap Density — By Increasing Water-retaining 
Capacity — Water-retaining Capacity Associated with Pentosan Content — 
Water Soluble Pentosans in Particular — Pentosan Content, Water-retaining 
Capacity and Hardiness Responsive to Environmental Conditions — In- 
creased Hardiness with Increased Maturity — Rapid Temperature Changes 
— Killing with Slow and with Rapid Freezing; Slow and Rapid Thawing — 
Variation in Critical Temperatures — Summary. 

CHAPTER XVI 

Winter Injury 264 

Conditions Accompany Winter Injury; Winter Injuries Classified — Injuries 
Associated with Immaturity — Affecting More or Less the Entire Plant — 
Tender Plants May be More Resistant Than Hardier Plants; the Effect of 
Summer Conditions Favorable for Late Growth ; Second Growth Particularly 
Susceptible; Preventive Measures — Localized Injuries — Crotch and Crown 
Injury; Localized Injuries and Delayed Maturity; Contributing Factors; 
Remedial Measures — Winter Injury Associated with Drought — Immaturity 
and Winter Drought — Water Loss from Dormant Tissues — Water Conduc- 
tion in Trees during the Winter — Relation of Freezing to Water Conduction 
— Where Winter Drought Conditions Prevail — Protection against Winter 
Drought Injuries — Winter Irrigation — Cultivation; Cover Crops — 
Windbreaks — Effect of Wind Velocity; Effect on Evaporation; Effect on Soil 
Moisture — Injuries Characteristic of Late Winter Conditions — The Rest 
Period — Injuries to Fruit Buds — Changes in Water Content of Buds during 
Winter — Contributing Factors — Protective Measures — Pruning; Fertiliza- 
tion and Cultivation; Thinning; Whitewashing and Shading — In General — 
Injuries to Vegetative Tissues — Distinguished from Summer Sunscald and 
Injuries Associated with Immaturity; Moisture and Temperature Condi- 
tions in the Affected Parts; Preventive Measures — Injuries Due to Sudden 
Cold — General Effects; Trunk Splitting — Summary. 

CHAPTER XVII 

Winter Injury to the Roots 302 

Soil Temperatures in Winter; Critical Temperatures for Tree Roots — Factors 
Influencing Frost Penetration — Protection Afforded by Snow; Different Sys- 
tems of Soil Management; Soil Type; Soil Moisture — Relation of Cover 
Crops to Root Killing — Root Killing in Different Fruits — The Apple; the 
Pear; the Peach; the Cherry; the Plum; the Grape; the Small Fruits — Pre- 
ventive and Remedial Treatments — Deep Planting and Mulching; Use of 
Hardy Stocks; Pruning; Handling Nursery Stock in Cold Weather — 
Summary. 

CHAPTER XVIII 

Winter Injury in Relation to Specific Fruits 318 

The Apple — Injuries Associated with Immaturity; Control Measures; 
Varietal Differences — The Pear; the Peach; the Cherry; the Plum; the 



xii CONTENTS 

Page 
Grape — The Small Fruit — Immaturity Most Important — Relation of 
Summer Pinching to Maturity; Varietal Differences from Year to Year — 
Injuries from Drought not Uncommon — Group and Varietal Characteristics 
— Summary. 

CHAPTER XIX 

The Occurrence of Frost 337 

Frost Formation — Frost and Freezes Distinguished — Relation of Radiation 
to Frost — Temperature Inversion; Radiation and Thermometer Readings; 
Radiation and Plant Temperatures — Dewpoint and its Relation to Frost; 
Relation of Clouds and Wind to Frost Occurrence— Influence of Location 
on Danger from Frost — The Blossoming Season and Latitude; Average 
Date of Last Spring Frost and Latitude; Average Dates and Frost Danger; 
Determining Frost Risks in Different Sections and Localities — Influence of 
Site on Minimum Temperatures — Minor Factors Affecting Temperature — 
Minor Differences in Elevation; Influence of Soil; Influence of Soil Covering; 
Influence of Soil Moisture; Effect of Cultivation; Significance, Particularly 
in Small Fruit Culture — Summary. 

CHAPTER XX 

Protection Against Frost 358 

Critical Temperatures — At Different Stages of Blossom Development; 
Varietal Differences; Vigor and Recuperative Ability; Weather Conditions 
before and after Freezing; Signs of Damage; Frost Injury and the Size of the 
Crop — Avoiding Frost through Late Blossoming Varieties — Blossoming 
Range Varies with Earliness; Blossoming Period and Fruit Bud Position; 
Retarding Blossoming; Indices to Blossoming Periods in New Locations — 
Frost Prediction — Relation of Dewpoint to Minimum Temperature; Weather 
Bureau Methods; Local Interpretation of Key Station Predictions — Frost 
Fighting — Smoke Screens to Reduce Radiation — Covering and Spraying — 
Orchard Heating — Heat Units in the Fuel; Height of the Ceiling Layer; 
Effect of Wind; Conditions Determining Practicability — Frost Effects — 
Summary. 

SECTION IV 
Pruning 

CHAPTER XXI 

Growing and Fruiting Habits 390 

Pruning for Form, Training — General Objects — Details in Training — Height 
of Head; Number of Scaffold Limbs; Distribution of Scaffold Limbs; Open 
and Closed-centered Trees; Trees of Different Shape; Lowering the Tops of 
Trees; Elimination and Subordinating Limbs; Preventing the Formation of 
Crotches — Bearing Habits — Relation of Growth Habits to Position of Fruit 
Buds; Different Kinds of Flower-bearing Shoots — A Classification of Plants 
According to Bearing Habits— Groups I-IX (Inclusive) — The Relation of 
Fruiting Habit to Alternate Bearing — Possible Causes of Different Bearing 
Habits — Summary. 



CONTENTS xiii 

CHAPTER XXII 

Page 

Pruning, the Amount or Severity 408 

Influence on Size of Tree — Amount and Character of New Shoot Growth; 
Leaf Surface and Root System — Influence on Fruit Spur and Fruit Bud 
Formation — Influence on Leaf Area and Fruit Size — Pruning as a Cause of 
Abnormal Structures — Amount of Pruning Varying with Fruiting Habit — 
Summary. 

CHAPTER XXIII 

Pruning, the Method ' 419 

Heading Back and Thinning Out — Influence on New Shoot and New Spur 
Formation; Influence on General Shape and Habit; Influence on Fruit Bud 
Formation and Fruitfulness; Thinning and Heading Lead to Different Nutri- 
tive Conditions; the Places of Thining and of Heading in Pruning Practice — 
Fine, as Compared with Bulk Pruning — Results following Dehorning; Re- 
sults Attending the Removal of a Few Large Limbs; Results Attending 
Spur Pruning; Application to Practice — Root Pruning — Special Pruning 
Practices — Summary. 

CHAPTER XXIV 

Pruning, the Season 438 

Pruning at Different Times during the Dormant Season — Summer Pruning 
— Influence on Vegetative Growth; Influence on Production; Summer Prun- 
ing to Develop Framework; Summer Pruning as a Conservation Measure; 
Influence on New Spur Formation; Influence on Fruit Bud Formation; 
Influence on Fruit Color — Summer Pinching — Summary. 

CHAPTER XXV 

Pruning with Special Reference to Particular Fruits 457 

Pruning the Apple and the Pear — The Formation of Fruit Spurs; Retaining 
Spurs Already Established; Keeping Spurs Strong and Vigorous; Summary 
of Usual Pruning Treatment; Special Suggestions for Unusual Fruiting 
Habits — Pruning the Peach — When and How Severely; Pruning to Secure 
Most Favorable Location of Fruiting Surface — Pruning the Sweet Cherry; 
Pruning the Almond, Apricot, Plum and Sovir Cherry; Pruning the Currant 
and Gooseberry; Pruning the Brambles — Pruning the Grape — Severity of 
Pruning; Kind of Pruning; Methods of Training. 

SECTION V 
Fruit Setting 

CHAPTER XXVI 

The Structures and Processes Concerned in Fruit Setting 475 

The Ovule — The Embryo Sac — Pollen — Pollination — Germination of the Pol- 
len Grain — Course of the Pollen Tube; Time for Pollen Tube Growth — 
Fertilization — Secondary Fertilization; Development of the Embryo and 



xiv CONTENTS 

Page 
Endosperm — The Setting of the Fruit — What Constitutes a Normal Set of 
Fruit — The June Drop and Other Drops — The First Drop; the Second Drop; 
the Third Drop or June Drop — Fruit Setting, Fruitfulness and Fertility 
Distinguished — Sterility and Unfruitfulness Classified — Summary. 

CHAPTER XXVII 

Unfruitfulness Associated with Internal Factors 489 

Due Principally to Evolutionary Tendencies — Imperfect Flowers, Dioecious 
and Monoecious Plants; Heterostyly; Dichogamy, Protandry and 
Protogyny; Impotence from Degenerating or Absorbed Pistils or Ovules; 
Impotence of Pollen — Due Principally to Genetic Influences — Sterility and 
Unfruitfulness Due to Hybridity — Incompatibility — Interfruitfulness and 
Interfertility; in Reciprocal Crossings — Due Principally to Physiological 
Influences — Unfruitfulness Due to Slow Growth of the Pollen Tube — Prema- 
ture or Delayed Pollination — Nutritive Conditions Within the Plant — Effect 
on Pollen Viability; Effect on Defectiveness of Pistils; Fruit Setting of 
Flowers in Different Positions; Strong and Weak Spurs; Evidence from 
Ringing Experiments; Evidence from Starvation Experiments — Summary. 

CHAPTER XXVIII 

Unfruitfulness Associated with External Factors 509 

Nutrient Supply; Pruning and Grafting; Locality — Season — End-season 
Fertility; Change of Sex with Season — Age and Vigor of Plant; Tempera- 
ture; Light; Disturbed Water Relations; Rain at Blossoming; Wind; Fungous 
and Bacterial Diseases; Spraying Trees When in Bloom; Other Factors That 
Cause the Dropping of Fruit and Flowers — Summary. 



CHAPTER XXIX 

Factors more Directly Concerned in the Development of the Fruit . . 521 
Stimulating Effects of Pollen on Ovarian and Other Tissues; the Effect of 
Certain Stimulating Agents on Fruit Setting — Seedlessness and Partheno- 
carpy — Seedlessness of Non-parthenocarpic Fruits; Vegetative and Stimula- 
tive Parthenocarpy; Relation of Anatomical Structure of Fruit to 
Parthenocarpy; the Value of Seedless and Parthenocarpic Fruits — The Rela- 
tion of Seed Formation to Fruit Development — Structure of Fruit; Form; 
Size; Composition and Quality; Season of Maturity; Specific Influence of 
Pollen on Resulting Fruit — Summary. 



CHAPTER XXX 

Fruit Setting as an Orchard Problem 538 

The Number of Pollenizers; Temporary Expedients; Pollinating Agents — 
The Fruit Setting Habits of Different Fruits — Apple; Pear; Quince; Peach; 
Almond; Plum; Apricot; Cherry; Grape; Strawberry; Currant and Goose- 
berry; the Brambles; the Nuts; Persimmon — Summary. 



CONTENTS XV 

SECTION VI 
Propagation 

CHAPTER XXXI 

Page 

The Reciprocal Influences of Stock and Cion 552 

The Congeniality of Grafts— Congeniality and Adaptability Distinguished— 
The Influence of Stock on Cion — Stature; Form — Seasonal Changes — End- 
season Effects, Ripening of Fruit; Maturity of Wood; Spring Effects— Hardi- 
ness— Disease Resistance— Physiological Diseases— Yield— Fruit-bud Form- 
ation; Fruit Setting; Size of Fruit— Quality— In Pomaceous Fruits; In 
Stone Fruits; in Grapes; Qualitative Differences and Quantitative Varia- 
tions — Longevity; General Influence of Stock on Cion — Influence of Cion 
on Stock — Size and Number of Roots; Distribution and Character of Roots; 
Longevity, Growing Season and Hardiness; Other Influences; in General. 

CHAPTER XXXII 

The Root Systems of Fruit Plants 584 

Conflicting Interests of Nurseryman and Fruit Grower — Adaptation of Stocks 
to Particular Conditions — Adaptation to Soil Temperatures; Adaptation to 
Soil Texture and Composition; Immunity or Resistance to Soil Parasites — 
Propagation by Cuttings — Advantages and Disadvantages — Grapes in 
Particular; Apples and Pears— Propagating Apples and Pears by Layerage 
and Hardwood Cuttings— Varietal Differences and Contributing Factors — 
Sources of Nursery Stock— Grades of Nursery Stock— Selection of Seedling 
Stocks; Grafted or Budded Trees; Double Worked Trees— Pedigreed Trees- 
Some Results in Citrus Fruits; Some Results in Apples; in General. 



SECTION VII 
Geographic Influences in Fruit Production 

CHAPTER XXXIII 

The Geography of Fruit Growing 612 

Life Zones, Crop Zones and Fruit Zones— The Boreal Zone; the Tropical 
Zone— Austral or Temperate Zone— Transition Zone; Upper Austral Zone; 
Lower Austral or Sub-tropic Zone— Geography of Fruit Production as Influ- 
enced by Temperature— Peach Growing as Influenced by Temperature; 
Grape Growing as Influenced by Temperature; Temperature and the 
Geographic Range of Apple Varieties; the Effect of Bodies of Water on 
Temperature; Influence of Altitude on Air and Soil Temperatures- 
Geography of Fruit Production as Influenced by Rainfall and Humidity — 
Other Factors Influencing the Geographic Distribution of Fruits— Sunshine; 
Parasites; Wind; Native Range of Parent Species; Length of Time in Culti- 
vation; Uses and Quality of Product; Relation to Consuming Centers and 
Transportation Facilities — Summary. 



CONTENTS 
xvi 

CHAPTER XXXIV Page 



Orchard Locations and Sites. . . . . , g g ' ' { Gr0 wing Section; Land 
Orcharding in or outside * Jjj™^ d Aspect _l n fluence on Soil Tern- 
Values; ^^T^t^XZTon Fruit Growing; Indirect 
peratures and on the Plant Speed* ^ f Elevation _Ther- 

Effects; Abruptness of Slope-A ^ r -T n fluence of Distance from Water; 
m al Belts-lnfluence ^«^% a £. Indirect Temperature Effects; 
Influence of Size and Shape otBodyo , Winter ; Obstructions- 

Minor Temperature ^^^^ ^ ture; Evaporation, Rainfall 
Local Variations and their Significance iei y 

and Other Factors— Summary. 



CHAPTER XXXV 



Orchard Soils. . . • • ■ ■ • ' ' " ' Phvsica i Condition— Requirements of 
Considered from the Standpoint of ^!%^ cat[on of Soils acc0 rding 
Different Crops; Requirements as to Depth C - Slhca ^ 
to Size of Soil Particles; Mechanical Analyse , otVa mentg 

Considered from the Standpoint of Chenncal Compoait 1 on q 

of Different Crops-Chenucal £*£,£ J^J^Vegetation 

dence on Soil ^^/^JT^ of Varieties to Particular 
as an Index to Crop Adaptation— Adaptation 01 



656 



as an Index to 

Soils— Summary. 



Glossary 
Index. . 



674 
679 



N 



THE FUNDAMENTALS OF 
FRUIT PRODUCTION 

SECTION I 
WATER RELATIONS 

The importance of moisture as a factor in the production of fruit 
is appreciated only in part. In arid sections the lack is obvious; in 
many regions certain lands are recognized as too moist for fruit plants. 
In the majority of the so-called humid sections, however, there is a 
tacit assumption that nature provides satisfactorily for the requirements 
of fruit plants. Drought may diminish or destroy other crops, but as 
long as trees survive there is considered to be sufficient moisture. 

The forest trees, relied on as evidence of this sufficiency, show, even 
in a limited area, striking differences in vigor, according to their locations. 
One of the most important factors recognized by the forester as affecting 
tree growth, is moisture. Certain spots even in humid regions, are 
chronically dry, some are nearly always wet; others, favorable in some 
seasons, are subject rather frequently to excess or deficiency of moisture. 

Much of the complacence concerning the water supply of trees is 
based on the supposedly great range of their roots and the consequent 
great amount of soil from which they can draw water. For this reason 
a statement of the extent to which forest trees actually deplete the soil 
moisture is pertinent. Zon 139 cites data showing moisture contents 
in June of 4.5 and 4.8 per cent, respectively at 4 and 8 inches in soil 
through which forest tree roots were ranging, while adjacent spots within 
the forest, exactly similar except that the roots had been excluded con- 
tained, at the same depths, 13.8 and 11.0 per cent, respectively. At 
16 inches the root free soil had over twice as much moisture as that to 
which the roots had access. Evidence is cited to the effect that the 
water level is lowered under forest and that with the removal of the forest 
the water level rises. Zon considers that the inability of many species 
to grow under an established cover of trees, commonly called shade 
intolerance, is in reality due to the low supply of moisture in the soil. 
When the roots of the top growth are excluded from an area, the intol- 
erant species grow there with considerable vigor. 

Deficient and excessive moisture are admittedly each a limiting 
factor in crop production. Table 1, based on estimates by crop reporters 

1 



2 FUNDAMENTALS OF FRUIT PRODUCTION 

of the United States Department of Agriculture, shows the damage 
caused by injurious moisture conditions in comparison with other factors. 
The figures on apples and berries are averages for the period 1912-1919 
and on other crops selected in comparison for the period 1909-1919. 
According to these estimates small fruits suffer more from drought than 
from any other single factor, while apples are injured more only by cold 
weather. 

Table 1. — Damage to Crops from Different Causes 

(After Smith 1 ") 





a 
u 
2 
m 
'o 

a 
« 1 

'S 

1 8. 

Q 


Excessive moisture, 
per cent. 


a 

a 
o 

ft 

■§ 
o 
o 

E 


<o 

M 

o a 

<D 

O <D 
»- ft 


a 
<u 
a 

h 

<u 
ft 

'3 

H 


a 

a 

M 

a 

ft 

•3 
a 

'$ 

o 

H 



aj 

h 

ft 

1 
u 

o 


ft 

u 

a 

03 

H° 8 


u 
o 

ft 

» 
03 

en 

s ° 


ft 

GO 

0) 

ft 

-^ • 

-; a 

m a 

a o 


u 

a 
ft 

-^ 

0) 

ft 

"3 

§ % 
< * 


(4 

ft 

01 

o 
J; 

.2 e 
Q S 


c 
o 

a 

ft 

"oS 
O 


Wheat 


12.4 
16.3 

6.7 
14.4 

8.7 
12.3 

5.4 

9.3 


2.0 
4.0 
3.1 
3.1 
3.7 
4.3 
1.6 
1.7 


0.3 
0.9 
1.5 
0.2 
0.6 
1.0 
0.2 
0.2 


4.5 
2.9 
0.3 
1.6 
1. 1 
1.4 
14.6 
7.3 


l.l 

0.4 

0.1 
0.8 
0.5 
0.8 
0.5 


2.0 
2.2 
0.4 
0.7 
0.2 
1.6 
0.5 
0.6 


0.3 
0.5 
1.8 
0. 1 
0.3 
0.7 
0.9 
0.2 


22.9 

27.7 
14. 1 
20.7 
15.8 
22.3 
24.9 
20.3 


2.7 
0.2 
1.2 
4.4 
0.4 
2.0 
3.7 
1. 1 


2.1 
2.7 
0.8 
3.2 
2.6 
9.7 
3.6 
0.6 


0.2 
0.2 
0.3 
0. 1 

0.1 
0.1 


0.2 
.0.7 
0. 1 
0.3 
0. 1 
0.2 


28.8 


Corn 

Rice 

Potatoes 


31.1 
19.0 
30.0 
20.5 


Cotton 

Apples 

Berries 


35.5 
39.6 
24.9 



Precipitation cannot be controlled. Soil moisture, however, is sus- 
ceptible more or less to modification by various practices and adjust- 
ments of fruits or of stocks for fruits can be made in some cases to the 
moisture conditions of the soil. For these reasons recognition of soil 
conditions, understanding of the water requirements of the various fruit 
plants and knowledge of the relation of various cultural practices to 
moisture control are of fundamental importance to the fruit grower. 



CHAPTER I 

THE WATER REQUIREMENTS OF FRUIT PLANTS 

There is more or less acknowledgement of a difference in adaptability 
of different fruits to varying moisture conditions in the soil; this is, 
however, expressed in terms of tolerance more often than in terms of 
requirements. It is stated frequently that sour cherries will stand a 
dry soil or that pears will endure a wet soil; there is very little exact 
information on what the various fruits actually require. Table 2 gives 
some interesting results of investigation in California on the requirements 
of fruit and other crops under conditions common in that section. The 
requirements of the several fruits stated in terms of the amounts of free 
water in the soil, exhibit a considerable difference. Other data to be 
introduced later (Tables 11 and 12) show that the same fruit may have 
different moisture requirements in different localities. 



Table 2. — Relative Water Requirements of Different Plants 

(After Loughridge* 7 ) 



Free water in 






4 feet of soil 


Plants for which the soil 


Plants for which the soil 






moisture is just above the 


moisture is just below the 






Percent- 


Tons per 


minimum; cultures did well 


minimum; cultures suffered 


age 


acre 






0.0 to 1.0 


80 


Apricots, olives, peaches, soy 
bean 


Citrus, pears, plums, acacia 


1 . to 1 . 5 


120 


Citrus, figs 


Almonds, apples 


1.5 to 2 . 


160 


Almonds, plums, saltbush 


Barley 


2.0 to2.5 


200 


Walnuts, grapes, eucalyptus 




2.5 to 3 . 


240 


Apples, prunes 


Prunes 


3.0 to4.0 


322 


Pears, hairy vetch 


Wheat 


4.0 to5.0 


400 


Wheat, corn 




5.0 to 6 . 


480 


Sugar beets, sorghum 


Sugar beets 



Water as a Plant Constituent. — Water is a normal constituent of all 
plant tissues, comprising from 50 to 75 per cent, of the leaves and twigs, 
from 60 to 85 per cent, of the roots, and 85 per cent, or more of most 
fleshy fruits. 

3 



4 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 3. — Typical Water Content of Fruit Plants in the Fall 129 



Fruit 



Flesh 



Skin 



Core 

or 
stone 



Stem 



Leaves 



New 
growth 



Old 
growth 



Apple 

Pear 

Peach 

Plum 

Cherry 

Currant. . . . 
Blackberry . 
Gooseberry . 
Raspberry . 
Grape 



85.64 
86.78 



89.74 
86.07 
88.78 
88.06 
89.98 



87.13 
85.10 
89.42 
84.35 

78.44 



85.81 
78.32 



85.71 
83.62 
32.67 
32.83 
46.81 



59.52 
68.76 

75.18 



53.00 
38.20 
63.78 
61.10 
65.10 
65.97 
48.14 
66.25 
33.28 
69.00 



49.40 
50.33 
49.52 
49.59 
49.51 
50.36 
38.15 
44.20 
41.33 
54.33 



45.74 
38.26 
39.77 
33.52 



Table 4 indicates the amounts of water found in various parts of the 
chestnut and walnut at different seasons and Table 5 shows the mois- 
ture content of bearing, non-bearing and barren spurs of the apple at 
various periods. All spurs have a maximum water content during or 
directly after the time of blossoming, but blossoming spurs contain 
much more water than spurs in the off year and these more than 
barren spurs. 



Table 4. — Typical Water Content of Roots, Branches and Leaves of the 

Chestnut and Walnut 3 



Chestnut 


May 30 


July 4 


Aug. 11 


Sept. 25 


Roots 


83.31 
78.68 
76.51 


66.12 
69.49 
71.44 


64.23 
51.69 

68.82 


59 82 


Branches 

Leaves 


53.32 

57.85 



Walnut 


July 31 


Sept. 15 


Nov. 6 




Roots 

Branches 

Leaves 


75.21 
68.30 
59.54 


69.54 
58 . 53 
52.00 


73.19 
68.43 
64.87 





Besides being a plant constituent, water is a plant nutrient and as such 
is indispensible for the manufacture of plant material, particularly in the 
photosynthetic production of carbohydrates. Finally, water is the 
medium in which all the nutrients essential to green plants, except carbon, 
occur in solution. 



THE WATER REQUIREMENTS OF FRUIT PLANTS 
Table 5. — Variations in the Water Content of Apple Spurs 68 





Feb. 


Mar. 


Mar. 


May 


June 


Sept. 


Nov. 


Jan. 




4 


11 


26 


13 


26 


2 


19 


24 


Bearing Spurs: 


















Wealthy 


49.9 






65.5 


61.1 


53.2 


50.5 


45.7 


Ben Davis 






60.0 


64.6 


61.8 


55.2 


51.6 


51.1 


Jonathan 




47.5 




63.2 


60.2 


54.8 


51.6 


47.7 


Non-bearing Spurs: 






















47.1 




54.8 


53.0 


51.4 


48.6 


49.6 


Ben Davis 






50.8 


59.8 


55.1 


48.6 


48.5 


48.9 


Barren Spurs: 


















Ben Davis 






45.6 


52.7 


47.8 


47.6 


44.6 


45.5 


Nixonite 


47.4 






56.2 


51.4 


47.6 


48.6 


43.1 



The Water Requirements of Plants in Terms of Dry Weight. — The 

water requirement of any plant is defined as the amount of water used 
while a unit weight of dry matter is produced. The weights may be 
measured in grams or in pounds, but the ratio obtained is the same in 
any case. Table 6 brings together data that have a bearing on this 
point, as reported by several investigators. 



Table 6. — Water Evaporated by Growing Plants for 1 Part of Dry Matter 

Produced 89 



Lawes and Gilbert 
(England) 



Hellriegel 
(Germany) 



Wollny 

(Germany) 



King 

(Wisconsin) 



Peas 235 

Barley 262 

Red clover 249 

Beans 214 

Wheat 225 



Peas 292 

Barley 310 

Red clover.... 330 

Beans 262 

Wheat 354 

Oats 402 

Buckwheat 374 

Lupin 373 

Rye 377 



Peas 479 

Barley 774 

Maize 233 

Millet 416 

Oats 665 

Buckwheat. . . . 664 

Rape 912 

Sunflower 490 

Mustard 843 



Peas 447 

Barley 393 

Red clover. . . . 453 

Maize 272 

Potatoes 423 

Oats 557 



Though Table 6 does not include figures for fruit plants it is presumed 
that as a class they do not differ materially from herbaceous plants in 
this respect. Hilgard 65 states that oaks require from 200 to 300 pounds 
of water for each pound of dry matter produced, while birches and lindens 
use from 600 to 700 pounds in producing 1 pound of dry leaves; the 
figures for beech and maple are intermediate. Hilgard estimates from 



6 FUNDAMENTALS OF FRUIT PRODUCTION 

30 to 70 units of water needed for the production of one unit of dry matter 
in spruce, fir and pine trees. Thus the range in water requirement for at 
least some of the ordinary deciduous trees is similar to that of herbaceous 
crops grown under similar conditions. 

Two striking points are shown by these figures on water requirements : 
(1) the great differences in the water requirements of different species 
and (2) the variation shown by the same plant in different sections, 
according to the determinations of different investigators. 

These differences carry two suggestions of practical import in fruit 
production; first, that certain species or certain fruits can do more than 
others with a given amount of water, second, that the same species of 
fruit plant will produce more vegetative growth with a given supply of 
water under certain conditions than under others. 

The Water Requirements of Plants in Terms of Precipitation. — 
Figures have been given showing the approximate water requirements 
of plants in terms of the number of units of water used while one unit of 
dry matter is produced. It is interesting to speculate as to what these 
figures mean in terms of rainfall or amounts of irrigation water. 

Amounts Used by the Plants Themselves. — Thompson 125 has calcu- 
lated the average weight of wood, roots and leaves produced by a normal 
healthy peach tree up to the time it has attained the age of 9 years as 
approximately 215 pounds. This represents an average annual dry 
weight production of wood, leaves and roots of approximately 25 pounds. 
With increasing age the amount would be somewhat greater. If a 300 
bushel per acre yield is assumed, it means the production of approximately 
20 pounds of dry matter per tree to be taken away in the form of fruit. 
In other words, the mature peach tree would be expected to produce 
about 45 pounds of dry matter per year. Assuming a stand of 100 trees 
to the acre this would mean a production of 4,500 pounds of dry matter 
per acre. If it takes 500 parts of water to produce one part of dry 
weight, it would require 22,500 pounds, over 11 tons or nearly 3,000 gallons 
per tree to mature the crop properly. This estimate considers only the 
amount actually taken up by the roots and for the most part transpired 
through the leaves and does not make any allowance for run-off from the 
surface, or for seepage and evaporation. It means 300,000 gallons per 
acre equivalent to a rainfall of approximately 11 inches, or an equivalent 
amount of irrigation water. For each additional 100 bushels of fruit 
per acre approximately 2 acre-inches more would be required by the 
plant. Looking at the matter from another angle, for every acre- 
inch under the 11 that is denied the trees, there would be a decrease in 
yield of approximately 50 bushels. Of course, if the water requirement of 
this fruit is only 300 instead of 500 under a given set of conditions, 7 acre- 
inches actually available to the trees would mature as large a crop as 
the 11 acre-inches in the first instance. 



THE WATER REQUIREMENTS OF FRUIT PLANTS 7 

That the first presented figures are probably representative for many- 
tree fruits is suggested by their close agreement with the 9 acre-inches 
estimate of Hilgard 66 as the water requirement of 15-year old orange 
trees in southern California and the 4,500 gallons per tree estimate of 
Duggar 43 as the requirement of a 30-year old apple tree. It is interesting 
to note that a 12-inch summer rainfall has been estimated as sufficient for 
the actual water consumption of 100-year old beech trees standing about 
200 to the acre." Data presented in Table 6 show that the variation in 
the water requirements of individual crops often exceeds the difference 
of 200 assumed in the case of the peach orchard. This emphasizes the 
point that it is frequently a matter of much practical importance to 
provide the tree with as nearly optimum nutritive conditions as possible, 
to secure the economical use of water if for no other reason. 

Total Amounts Required for Plants and to Compensate for Evaporation 
Run-off and Seepage. — It should be noted that in the last paragraph when 
7 to 11 acre-inches of water was mentioned, as approximately the amount 
required to mature a peach crop of a certain size, reference was made 
only to the water actually taken up and used by the plant. As is well 
known, a considerable percentage of the water that reaches the land as 
rain or snow or through the irrigation channel is made unavailable by 
run-off, evaporation and seepage. The exact percentages removed in 
these ways vary greatly, depending on the seasonal distribution of the 
rainfall, the topography, the character of soil and subsoil, the atmos- 
pheric humidity and other factors. It has been estimated that in the 
forest, where conditions are more favorable than in most fruit plantations 
for the reduction of run-off and evaporation, probably not more than 35 
per cent, of the precipitation actually becomes available for tree growth. 18 
In orchard practice then, it is doubtful if much more than one-third of 
the natural precipitation or irrigation water can be considered to be 
utilized by the trees, and under poor methods of soil management or in 
soils of poor water-absorbing and water holding capacity the percentage 
may be much lower. 

In the light of what has been said it obviously would be impracticable 
to attempt the construction of a table showing the rainfall requirements of 
different fruit crops, such as strawberries, cherries, apples and olives, for 
there are too many contributing factors to be evaluated, but the general 
principles that have been given should be capable of interpretation and 
intelligent application to many concrete practical problems as they arise 
in orchard management. For instance, with a fairly accurate knowledge 
of the mean and minimum rainfall of a particular location and its seasonal 
distribution, and after a first hand study of soil conditions as they relate 
to moisture, it should not be difficult to determine more or less accurately 
the practicability of growing a certain fruit crop without irrigation 
facilities, or to determine the relative importance of certain moisture 



8 FUNDAMENTALS OF FRUIT PRODUCTION 

conserving practices. Experience may be a still better guide but only 
to the extent that it gives ability to judge local conditions and so permits 
a more accurate interpretation and application of general principles. 

Some measure of the way these principles apply to concrete cases 
may be obtained from the statement that it has been found practicable 
to use irrigation water amounting to about 30 acre-inches for mature 
peach trees on some of the gravelly loams of Utah and 40 acre-inches on 
full bearing apple orchards on sandy loam in Idaho where rainfall aver- 
aged 10 or less inches per year. On the other hand, heavy crops of sweet 
cherries, prunes and apricots are obtained without irrigation from 
orchards on a light sandy loam at The Dalles, Ore., with an average 
annual rainfall of 16 or 17 inches. 

Some years ago 16 or 18 inches of rainfall annually was generally 
considered sufficient for the production of deciduous fruits in California, 
but experience has demonstrated that the percentage of this amount 
that is actually left for the trees after run-off, seepage and evaporation 
is not adequate for the average orchard with the trees spaced the usual 
distances. As a matter of fact there is a growing belief that even a 
rainfall of 30 inches in California should be supplemented by provision 
for irrigation to take care of occasional emergencies. 127 

Planting Distances Related to Moisture Supply. — Application of the 
principles just pointed out to particular fruits and particular locations 
should be the main deciding factor in determining distance of planting for 
orchard fruits, for water supply is most frequently the limiting factor in 
this connection even though the grower seldom realizes it at the time of 
setting. This is contrary, in the way it often works out, to the frequently 
repeated statement that trees can be planted more closely in a "poor" 
than in a "good" soil. If the soil is "poor" because it is shallow or of 
poor water-holding capacity unproductiveness will only be increased by 
closer spacing. In soils that are both fertile and well-watered, planting 
distance should be governed by the size of the plants and the growing 
habit. If they are infertile and well-watered, again planting distance 
should be determined by size of plant and growing habit, and the fertility 
question solved through the proper use of fertilizers. If moisture is the 
limiting factor, regardless of the relative productivity of the land, spacing 
should be determined largely by moisture requirements, though due 
attention should be given to growth characteristics. 

A notable instance of the intelligent and successful application of these 
principles to the question of planting distance is found in some of the olive 
orchards of northern Africa. Though the usual planting distance for this fruit 
in irrigated sections, or in regions of ample rainfall is 18 to 22 feet, near Sfax in 
Tunis the trees are planted 60 to 80 feet apart, making only 7 or 8 to the 
acre. This arrangement makes possible a profitable dry-land industry without 
irrigation, though the mean annual rainfall is only 9.3 inches and though there 



THE WATER REQUIREMENTS OF FRUIT PLANTS 9 

are often several successive years in which the total precipitation does not 
exceed 6 inches. 75 

Another interesting application of the same principle has been recorded in 
South Dakota. Cottonwoods planted rather close together for windbreak or 
shelter belt purposes, thrive for a number of years, but eventually a stage is 
reached when they begin to die from crowding. If wider spacing or thinning is 
practiced their longevity is increased correspondingly. 36 

Factors Influencing the Water Requirements of Plants. — It is advisable 
at this point to review some of the data available on the economy with 
which the plant uses water. From what has been said regarding the total 
water requirements of the plant it is evident that only an extremely 
small percentage is finally held by the plant as a constituent of the proto- 
plasm or is used in the manufacture of chemical compounds. The 
greater portion of the water has been required to meet evaporation. 
Since the water requirement is a ratio between the water used and the 
plant material produced, it is evident that all other factors favoring the 
nutrition of land plants will tend to decrease their water requirement and 
that all factors tending to increase water loss through transpiration 
will increase it. Experimental evidence bearing on the factors affect- 
ing nutrition is available, but the effects of factors altering water loss 
have not been so thoroughly studied. 

Nutrient Supply. — Table 7 shows the mean water requirements of 
oats and wheat as influenced by fertilizer treatments and Table 8 presents 
data showing the effects of various amounts of nitrogen upon the water 
requirement of the plant. 

It is a reasonable assumption that when the soil solution is poor in 
any indispensible element more water must be taken up by the plant to 
obtain an ample amount of this element. However, this is true only 
within certain limits, because of the ability of plants to withdraw from 
the soil nutrient materials in proportions quite different from those in 
which they occur there. Attention has been called to the considerably 
higher water requirement of plants in the very rainy climate of Munich, 
Germany, than in the drier portions of northern Germany or in Wis- 
consin. It is suggested that as the moisture approaches the extreme in a 
wet soil the soil solution is diluted; hence conditions are presented that at 
least in a way are comparable with those found in a "poor" soil. More 
water is required to absorb a given amount of nutrients. Possibly in this 
case the poor aeration attendant upon a soil moisture content above the 
optimum may also affect the water requirement. The effects of a very 
dry soil, which likewise increases the water requirement, is attributed by 
Briggs and Shantz 21 to the restricted area which the active roots and root 
hairs occupy under these conditions. It seems a strange perversity of 
fate that the soil conditions and soil treatment which are most likely to 
result in a restricted root system, such as heavy soils, hardpan, water- 



10 



FUNDAMENTALS OF FRUIT PRODUCTION 



logging, puddling and baking, are those which lead to an increased water 
requirement of the plant. 

Table 7. — Mean Water Requirements of Oats and Wheat with Different 

Fertilizer Treatments 

{From determinations made by Liebacher, Von Seelhorst, Bunger and Ohlmer 21 ) 

Mean Water Require- 
ments for Oats 
and Wheat 



Fertilizer 

KN P . 

N P.. 
NK.. 

N.. 
P K.. 

P. 
Check.. 

K . 



238 
243 
246 
259 
294 
297 
308 
314 



Table 8. — Effects of Various Amounts of Nitrogen on the W'ater Require- 
ment of Plants 

(After Hellriegel 62 ) 



CaN0 3 supplied 
(grams) 


Dry matter 

produced 

(grams) 


Water 
transpired 

(grams) 


Water 
requirement 


1.640 
1.312 
0.984 
0.656 
0.328 
0.000 


25.026 
23 . 026 
18 . 288 
13.936 
8.479 
1.103 


7451 
6957 
6317 
4839 
3386 
956 


292 
302 
345 
347 
399 
867 



Cultivation. — Bearing directly on this point are data obtained on the 
effects of cultivation in lessening the water requirements of plants. Some 
of these data are presented in Table 9. In every case the water require- 

Table 9. — The Influence of Cultivation Upon Water Requirements of Plants 

in Different Soils 136 



Not cultivated 



Cultivated 



Sandy loam 

Clay loam 

Clay 

Type not given 




252 
428 
582 
265 



ment was materially reduced by cultivation; in one case it was more than 
cut in two. In certain soils the influence of cultivation was much more 
pronounced than in others. Presumably cultivation affects the water 



THE WATER REQUIREMENTS OF FRUIT PLANTS 



11 



requirements of plants by increasing both the moisture content of the soil 
and the supply of available plant nutrients. 

Light. — It should not be inferred from what has been said, that the 
plant's water requirement is entirely governed by its nutrition. Investi- 
gation has shown, for instance, that in tobacco, the amount of water 
absorbed is quite independent of the amount of mineral constituents 
taken in. 58 Thus the average ratio of water to ash for six plants grown 
in the open was 2,548, while for six plants grown under shade it was 1,718. 
These data, however, apply only to the water-ash ratio of plants growing 
in full sunlight and in shade. For the water-dry-matter ratio in sunlight 
and shade a somewhat different condition holds, probably because of the 
influence of the sunlight in promoting photosynthetic activities and the 
storage of elaborated materials. 

Table 10. — Water Requirements per Unit op Dry Weight of Leaves in Sun and 

Shade 

(After H6nel*») 

(Kilograms per 100 grams of dry leaves) 



Species 


Sun 


Shade 


Beech 


76.18 
81.30 
61.69 
19.15 
13.91 
8.76 


107 80 


Hornbeam 


98 90 


Sycamore 


76 19 


Scots pine 


5 02 


Silver fir 




4 85 


Black pine 




5 25 









Data presented in Table 10 show that in all the broad-leaved trees 
studied, the water-dry-matter ratio rose in the shade, though with the 
conifers it was greatly lowered. The data on tobacco alone might 
suggest that with the nutrition factor constant more water would be 
required in exposed than in protected situations and that shading and 
windbreaks might be expected to reduce materially the plant's water 
requirements. On the other hand, the data of Hasselbring and Honel 
together lead to the inference that though the mineral requirements of the 
plant as related to water supply may be increased in exposed and de- 
creased in protected situations, tissue building and the manufacture 
and storage of elaborated materials may be promoted by the opposite 
conditions. 

In General. — Recent investigations by Briggs and Shantz 22 lead 
them to conclude that when a crop is thoroughly adapted to a certain 
environment it has its water requirement at the minimum and that its 
water requirement gradually increases as it is forced to grow in more 
and more uncongenial conditions, whatever they may be. Thus as a 



12 FUNDAMENTALS OF FRUIT PRODUCTION 

rule, cool weather crops have a lower water requirement in a cool than 
in a warm climate, the reverse being true of warm weather crops. In 
the latter instance, however, the difference is less pronounced, due to 
the effect of increase in temperature upon transpiration in general. 

As will be shown later, however, plants are able to adapt themselves 
in certain ways to dry conditions, the result being a lowering of what 
otherwise would be a very high transpiration rate. Only limited data 
are available as to how these tendencies balance each other and as to 
what is the final resultant. Leather 83 has found that at Pusa, India, 
the water requirements of wheat, barley, oats and peas are nearly twice 
those of maize, though this ratio does not hold in most sections (see 
Table 6). Apparently this high water requirement of these cool season 
crops is associated with their maturing during the dry season, while 
in India maize matures during the more humid season of the monsoon. 
The greater water requirement of plants cropped by means of pasturing 
as compared with that of plants which are allowed to continue their 
growth uncropped, 130 may be taken as an indication that new growth 
has a higher water requirement than older growth. It would seem that 
the water requirements of different plants vary mainly because of differ- 
ences in the economy of their nutrition and because of different physio- 
logical and structural modifications affecting their rate of transpiration. 

Some Applications to Practice. — The influence of both the chemical 
and the physical conditions of the soil upon the water requirement 
of the plant is of practical importance to the grower, the influence of 
soil productivity being particularly significant. Few realize that, when 
the soil provides conditions for tree growth that are optimum from the 
standpoint of nutrient supply, actually less water is required for a given 
yield than when the plant is handicapped because of the lack of some 
nutrient as well. This difference in water requirement is not one of 
academic interest only; it is large enough frequently to account for crop 
failure or crop success under conditions of limited water supply. 

A quotation from King 79 is to the point: "In the long series of studies made 
by the writer on the amounts of water required for a pound of dry matter, it was 
found true, almost without exception, that strong vigorous growth and high 
yields of dry matter are always associated with a small transpiration of water 
when measured by the dry matter produced." 

Even more significant is the statement of Leather, 83 who made a careful 
study of this question in the dry climate of Pusa, India: "The effect of a suitable 
manure in aiding the plant to economize water is the most important factor 
which has yet been noticed in relation to transpiration." 

It would probably be a mistake to advise watering or irrigating trees 
by fertilizing them, because the advice would be taken too literally. 
Nevertheless, the reduction of the water requirement of the plant by 
maintaining the soil in a condition as near as possible to the optimum 



THE WATER REQUIREMENTS OF FRUIT PLANTS 13 

with respect to nutrient supply should be a constant and conscious aim 
in scientific orchard management, though perhaps the water conservation 
influence of optimum growing conditions may be more or less masked 
by the increased requirements for the accompanying increased growth. 

The Wilting Point for Fruit Plants. — There seems to be some differ- 
ence of opinion as to how near to the hygroscopic coefficient plants can 
exhaust the water supply of the soil. Loughridge states that certain 
plants can remove enough of the hygroscopic moisture of the soil to 
maintain life though they cannot grow under these conditions; Hilgard 
states that soils of great hygroscopic power can withdraw from moist 
air enough moisture to be of material help in sustaining the life of vegeta- 
tion in rainless summers or in time of drought, though only a few desert 
plants can maintain normal growth. 64 In most plants, however, wilting 
will occur before the moisture content of the soil has been reduced to its 
hygroscopic coefficient. 

Wilting Coefficients. — The work of Briggs and Shantz 20 has led them 
to conclude that the wilting coefficients for most soils equal their 

o fiR 4- 019 Thus a sandy loam with a hygroscopic coeffi- 
cient of 3.5 per cent, would have a wilting coefficient of about 4.8 and a 
clay loam with a hygroscopic coefficient of 11.4 would have a wilting coeffi- 
cient of 16.3 per cent. These investigators state, "The wilting coeffi- 
cient is the same, within the limits of experimental error, for a plant in 
all stages of development. In other words, the soil-moisture content 
at the wilting point is not dependent to any material degree upon the 
age of the plant. . . . [It] is not materially influenced by the dryness of 
the air, by moderate changes in the solar intensity, or by differences in the 
amount of soil moisture available during the period of growth." 20 It 
ranges for different soils from less than 1 per cent, in the coarsest sands 
to as high as 30 per cent, in the heaviest clays. "The use of different 
plants as indicators of the wilting point produces only a relatively small 
change in the wilting coefficient of a given soil. Representing the mean 
value of the wilting coefficient of a given soil by 100, a range from 95 
to 105 approximately, would result from the use of different plants 
as indicators. . . . The xerophytes tested gave a mean ratio inter- 
mediate between the hydrophytes and mesophytes. This would indicate 
that plants native to dry regions are unable to reduce the water content of 
the soil to a lower point at the time of wilting than is reached by other 
plants. . . . There is evidence that drought resistance in a plant is not 
due to an additional water supply made available for growth by virtue 
of a greater ability on the part of that plant to remove moisture from 
the soil." 20 

Wilting Under Field Conditions. — The work of Briggs and Shantz on 
wilting coefficients of different soils was done, however, under fairly 



14 FUNDAMENTALS OF FRUIT PRODUCTION 

uniform conditions of temperature (about 70°F.) and humidity (about 
85 per cent.), conditions under which the evaporating power of the air 
is low. In other words the plants exhausted the water supply of the 
soil slowly and because of favorable atmospheric conditions were actually 
able to use the last of the "available" moisture before transpiration 
demands overtook absorption. In the field, wilting does not usually 
occur under such favorable atmospheric conditions — favorable from the 
standpoint of soil moisture supply. 

It has been found that when atmospheric conditions are such as to promote 
rapid evaporation, "the departure of observed from calculated soil moisture 
contents at permanent wilting is extremely marked for all soils; permanent 
wilting in the open occurs with a soil moisture content from 30 to 40 per cent, in 
excess of that present when the same or similar plants are wilted in a moist 
chamber. . . . Marked increase in the evaporating power of the air acceler- 
ates the outgo of water without producing a proportionate increase in its rate of 
entrance from the soil. With every increase in transpiration rate above a 
certain limit, this rate becomes, therefore, more and more significant as a factor 
determining the extent to which the soil water may be exhausted by the plant 
before the advent of permanent wilting. Thus, permanent wilting under high 
rates of evaporation does not at all indicate that the available soil moisture 
has been exhausted. Instead, it merely indicates the reduction of the soil 
moisture content to a magnitude which corresponds to the residue of water left 
in the soil at the time when excess of transpiration over absorption has brought 
the entire plant into the permanently wilted condition. Repeated determi- 
nations, under widely varying conditions but with relatively high evaporation 
rates, show that the magnitude of this residue is directly related to the intensity 
of the evaporating power of the air." 31 

It is these higher wilting coefficients under the comparatively high 
transpiration rates of midsummer which interest the deciduous fruit 
grower most frequently. Perhaps the wilting coefficient based upon soil 
texture and calculated for low transpiration rates is most important in 
determining whether the plant shall or shall not survive the period of 
drought, for before death occurs there usually will be a shedding of 
foliage and other protective measures will be taken to reduce moisture 
requirements and lower the transpiration rate. On the other hand the 
effects of drought upon the vegetative activities of the tree during the 
summer, upon the size of its fruit and upon the abscission of its leaves, 
flowers and partially grown fruit are exercised during periods of very 
high transpiration rates. This means that correspondingly high wilting 
coefficients prevail and that the aim of the grower should be, as far as 
possible, to maintain the moisture supply of the soil well above these 
higher amounts. 

Wilting Coefficients and Drought Resistance. — Tables 2, 11 and 12 
compiled by Loughridge, showing the minimum water requirements of 



THE WATER REQUIREMENTS OF FRUIT PLANTS 



15 



certain fruits in comparison with those of certain other plants, are par- 
ticularly interesting in this connection. 

Table 11. — Minimum Water Requirements op the Apricot in Different Soils" 
(Records made in early September) 



Soils 



Locality 



Condition of 
trees 



Moisture in 4 feet of soil (per cent.) 



Total 



Hygro- 
scopic 



Free 



Tons of free 

water per 

acre 



Dark loam. . . 
Loam 

Loam , 

Loam 

Sand 

Loam 

Loam 

Loam 

Loam 

Black clay. . . . 
Gravelly loam 

Sand 

Alluvial . 



Sisquoc Valley . 

East of Ventura (shallow 
cultivation) 

Ventura (shallow culti- 
vation) 

Ventura (deep cultivation) 

Los Berrios Hill 

Experiment station 

Niles (no cultivation) 

Niles (cultivation 3 inches) 

Niles (cultivation 6 inches) 

Woodland 

Woodland 

East of Davisville 

Davisville 



Good 


5.5 


3. 1 


2.4 


Growth 6 inches 


6.5 


5.5 


1.0 


Growth 8 inches 


5.6 


4.2 


1.4 


Growth 36 inches 


9.3 


5.5 


3.8 


Good 


1.7 


0.8 


0.9 


Good 


6. 1 


5.0 


1. 1 


Very poor 


4.4 


4.4 


0.0 


Fair 


5.4 


3.3 


2.1 


Excellent 


6.3 


3.3 


3.0 


Excellent 


18.8 


9.6 


9.2 


Poor 


6.9 


5.0 


1.9 


Good 


4.8 


3.6 


1.2 


Good 


9.0 


6.9 


2. 1 



80 

112 

304 

72 

88 



168 

240 

736 

152 

96 

168 



In commenting upon these tables Loughridge states: "The apricot, olive 
and peach do well on less water than other orchard fruits, 1 per cent, of free 
water being sufficient if constantly present. With this amount the citrus fruits, 
pears and plums were found to suffer, though the citrus fruits were in good con- 
dition with a little more water. The almond seems to require about twice the 
water that the apricot does, while the prune was found to suffer with three times 
the water in which the apricot was nourishing. 

" Emphasis should be placed on the fact that this free water should be present 
throughout the soil to the depth of 4 feet at least and especially around the 
feeding rootlets of the tree. The surface of the soil may be wet, and yet the 
tree may suffer if the ground below be so dry that the rootlets are not able to 
draw sufficient moisture. This drying-out of the under-soil is one of the evil 
effects of a severely dry season, and unless the rainfall of the succeeding winter be 
sufficient to penetrate to the depth of several feet and moisten the soil around 
the rootlets the trees will suffer "almost as if no rain had faUen. The same is 
true with regard to irrigation ; those who have to resort to the artificial application 
of water to their lands because of insufficient rainfall, should so apply it that it 
may reach the tree rootlets at the depth of several feet below the surface. This 
is too often not done, and examination will show that the water has, even after 
2 days' irrigation with running water in furrows, not soaked down more than 10 
or 12 inches, if that much." 87 

At first, it may seem that the field observations of Loughridge are 
not in agreement with the conclusion of Briggs and Shantz that the 
wilting coefficients are practically the same for all plants growing in the 



16 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 12. — Relative Water Requirements of Different Fruits in Different 

Soils 
{After Loughridge 87 ) 



Free water in 
4 feet of soil 


Plants for which the soil 

moisture is just above the 

minimum; cultures did well 


Plants for which the soil 
moisture is just below the 
minimum; cultures suffered 


Percen- 
tage 


Tons per 
acre 


Sandy soils — hygroscopic moisture 1 to 3 


2.0 

2.5 
3.5 


160 
200 
280 


Apricots, saltbush 
Olives, peaches, wheat 


Olives, peaches, plums, grapes 
Cherries, pears 
Citrus, prunes 






Sandy loam soils — hygroscopic moisture 3 to 5 


4 to 5 

5 to 6 


400 
480 
560 
640 
720 


Saltbush 
Apricots 


Apricots 


6 to 7 


Prunes 


7 to 8 


Almonds, plums 
Apples, olives, peaches, 
walnuts 




8 to 9 












Loam soils — hygroscopic moisture 5 


4 to 5 

5 to 6 

6 to 7 

7 to 8 


400 
480 
560 
640 
720 
800 


Saltbush 

Apricots, citrus, figs, walnuts 

Prunes, grapes 


Apricots, almonds 
Prunes 


8 to 9 


Apples 


Almonds 


9 to 10 
















Clay loams — hygroscopic moisture 5 to 7 


6 to 7 

7 to 8 

8 to 9 


560 
640 
720 


Peaches, grapes 


Peaches, plums 
Wheat 
Sugar beets 






Clay soils — hygroscopic moisture 7 to 10 


8 to 9 

9 to 10 


720 

800 

880 

960 

1120 


Apricots 
Grapes 


Figs 


10 to 11 


Wheat 


11 to 12 




Citrus 


12 to 14 


Corn, sugar beets 









THE WATER REQUIREMENTS OF FRUIT PLANTS 17 

same soil. The greater tolerance of the apricot, olive and peach for drought 
probably is not due to a utilization of the soil water in contact with their 
roots greater than that of other plants, or in other words, to the reduction 
of the soil water content to a lower wilting coefficient. It is possibly 
associated with a greater ability of their roots to exploit every bit of soil 
within their range, or to a wider range that their roots may possess. 
It is important that both factors be kept in mind, namely, the marked 
uniformity in the wilting coefficient for different plants and the marked 
difference in their ability to get along on a limited water supply, for 
both are factors that may alter materially cultural methods, the choice 
of stocks upon which the fruits are grown and planting plans. As a rule 
it is not necessary to wait until wilting actually begins to determine when 
the danger point is at hand. Most plants will show signs of distress 
before the moisture supply of the soil reaches its wilting coefficient. 
Many weeds or cover crop plants growing among the trees may wilt 
noticeably before the trees give visible evidence of moisture deficiency. 
Temporary wilting at the middle of the day is quite likely to be an indica- 
tion that the water supply of the soil is approaching a critical point and 
efforts should be made to deal with the situation promptly. 

Summary. — Water is an important plant constituent, composing 
from 50 to 85 per cent, of most living tissue. It is the solvent for all 
plant nutrients. The intake of from less than 30 to more than 1,000 parts 
of water is required for each part of dry matter produced, the amount 
varying with the species and with the conditions under which the plant 
is grown. When seepage, run-off and evaporation are included this 
means that for the average deciduous fruit crop a precipitation of some- 
thing like 30 inches is required. Inability to secure the requisite amount 
of water checks growth and reduces yield and often a relatively small 
amount of additional available moisture at a critical period will make 
possible material increases in the size of the crop. Planting distances 
in the orchard should be determined largely by the available moisture 
supply and the growing habits of the particular species or variety. The 
minimum water requirement of the plant, in terms of units of water 
per unit of dry matter, is correlated with thorough acclimatization and 
optimum growing conditions. Favorable nutritive conditions in particu- 
lar make for water economy. The final wilting coefficient is practically 
the same for all plants in all soils, but it varies greatly for the same plant 
with different soils, being low for soils of coarse texture and very high 
for fine clays. In the field, temporary wilting generally occurs before 
the wilting coefficient is reached, the evaporating power of the air being 
an important determining factor. In practice it is therefore desirable 
to maintain the soil moisture supply well above the wilting coefficient. 
Different species and varieties show considerable variation in their 
ability to withstand drought. 



CHAPTER II 

THE INTAKE AND UTILIZATION OF WATER 

Under favorable conditions the entrance of water into the plant, 
its translocation and its egress take care of themselves, without conscious 
manipulation by the grower. At times, however, one or another of 
these processes should be controlled to some degree and pathological 
symptoms or conditions may arise which can be understood only through 
a knowledge of these processes. 

WATER ABSORPTION 

Proper absorption, as the necessary prelude to the other processes, 
is of obvious importance. Furthermore, it is the process with which the 
grower is most frequently brought into contact. 

The Water Absorbing Organs. — The root is the absorbing system and 
for practical purposes all the water which enters the plant is absorbed 
through the root. There are indeed other sources from which moisture 
can be obtained, such as, for example, the water resulting as an end prod- 
uct of the oxidation of carbohydrates, which has been termed metabolic 
water, 6 but such sources are significant only in extreme circumstances. 
The absorption of water by the root takes place chiefly through special 
structures, the root hairs, which are extensions from the epidermal cells 
of the root a short distance back of the growing point. The absorption 
power of the root depends upon the extent of its surface and it is increased 
to a marked degree by the presence of root hairs. The ratio of the 
surface of the root supplied with hairs to one from which the hairs have 
been removed has been calculated as 5.5 : 1 for maize and in the garden 
pea 12.4 : l. 109 These figures give some idea of the efficiency of the root 
hairs for water absorption. Moisture can be absorbed by the root tip 
and also through the surface of the root for some distance above the zone 
of root hairs. In the older portions of the root the cortex and epidermis 
die and peel off as a result of the formation of deep seated cork; hence, 
this portion of the root is incapable of absorbing appreciable amounts 
of water. 

The number of root hairs varies with different plants and, in the same 
plant, with the conditions under which it grows. Thus, the development 
of root hairs is reduced in wet soil, or in very dry soil and may be entirely 
prevented where the root is in contact with water. 55 This occurs in 
certain plants, such as the cranberry, which normally grow in bogs where 
the roots do not develop root hairs. 

18 



THE INTAKE AND UTILIZATION OF WATER 19 

The Handling and Transplanting of Nursery Stock. — The practical 
bearing of the point just brought out upon the transplanting of fruit 
trees or other plants is important. The transplanting of most deciduous 
fruit trees and of many other plants is usually accompanied by the loss 
of a considerable part of the large and of the fibrous roots and by the 
destruction of practically all of the root hairs. New root hairs must be 
produced before active absorption can begin; these new root hairs will 
be formed only on new branch rootlets. This means that if the top of 
the plant has any considerable water requirement at the time of trans- 
planting it will suffer for lack of moisture and perhaps wilt and die if new 
roots are not formed immediately. The grower is likely to place a rather 
high premium upon a large and extensive root system in nursery trees, 
thinking that they will surely absorb enough water to maintain the 
moisture supply of the tops until new roots are formed. A fairly ex- 
tensive root system in the nursery tree may be an asset, but not because 
these roots devoid of root hairs are of any material aid in the direct 
absorption of water. This explains why tree roots pruned according to 
the so-called Stringfellow method at the time of setting are usually as 
sure to take root and grow as those pruned less severely, though the 
subsequent growth may not be so satisfactory. More important still, 
it explains also why it is desirable to prune back the tops of most plants 
at the time of transplanting so as to reduce transpiration to a minimum 
and prevent desiccation. It shows furthermore why in climates not too 
cold, fall transplanted trees are more likely to give a good stand than 
corresponding spring-set trees, for during the winter months new root 
formation is initiated and water can be absorbed in the spring as fast as 
the new shoots and leaves use it. 135 The spring-set trees, on the other 
hand, must wait until new roots are formed before th'ey can take up 
moisture and if soil conditions remain unfavorable for this root formation 
and atmospheric conditions stimulate vegetative growth of the top, the 
pushing shoots will wilt and die, and the tree will be lost. In the autumn 
conditions are favorable for root growth for some time after good growing 
conditions for the top have passed ; in the spring they frequently become 
favorable for top growth before or simultaneously with suitable growing 
conditions for the roots. 

In the light of the facts presented it is not difficult to understand why the 
transplanting of trees after their buds have once started in the spring is 
attended with very uncertain results. It is simply a case of a demand 
for water for supplying the top, great in comparison with the demand 
while in the dormant stage, a demand that cannot be met by the roots 
because, temporarily, they are practically without absorbing organs. If 
it is necessary to plant trees late in the spring, after some vegetative 
growth may be expected to take place, it is well to remember that the 
transplanted tree will have practically no root hairs for several days or 



20 FUNDAMENTALS OF FRUIT PRODUCTION 

even weeks after the transplanting operation and that, therefore, the 
tree must be kept practically dormant until it is actually planted. This 
may be done by holding it at a low temperature in shade, or, if suitable 
storage facilities are not available, by repeatedly lifting and immediately 
heeling in again. The effect of the low temperature is to keep the tree 
dormant because no top growth will take place at a temperature approxi- 
mating the freezing point. The effect of the repeated lifting and heeling 
in again is to check growth of the top by preventing the formation of new 
roots and root hairs though the temperature may be suitable for their 
development and thus cutting off the tree's water supply without which 
the shoots are retarded. 

It is necessary to move evergreen trees of any considerable size, like 
the pine or the orange or the avocado, with a ball of earth so that at least 
a moderate portion of the real water absorbing organs of the plants are 
retained and remain active; otherwise, the foliage wilts or falls off and 
the plant is likely to die. The facts that have been presented explain 
why excessive watering will not make up for the loss of roots, and particu- 
larly of root hairs, by trees transplanted during their growing season. 
Though their remaining roots may be surrounded by a nearly saturated 
soil they cannot take up appreciable quantities of this moisture. 

The Water Absorbing Process. — The process by which water is absorbed by 
the root hairs is osmosis. A plant cell such as the epidermal cell of a root with a 
root hair attached has a cell wall lined with protoplasm surrounding a central 
vacuole. When the root hair comes in contact with the moisture of the soil an 
osmotic system is established and the protoplasm of the root hair becomes a 
semi-permeable membrane separating two solutions, the soil solution on the 
outside and the vacuole on the inside. These two solutions have different 
concentrations, that of the vacuole being greater than that of the soil solution; 
in other words there is less water in the vacuole than in a corresponding volume 
of soil solution. To equalize the concentrations of water on either side of the 
membrane water passes from the soil into the vacuole. 

The absorption of water in this way by the cell must increase the size of the 
vacuole and therefore induce a simultaneous distention of the cell wall. Eventu- 
ally the elasticity of the cell wall will exert such a pressure on the vacuole that 
no more water can be absorbed and there is a balance between the elasticity of 
the cell wall and the osmotic pressure of the cell contents; the cell is in a state of 
turgidity. Under ordinary conditions all the living cells of a plant are turgid, 
but this turgidity may be lost, either by an increase in the plasticity of the cell 
wall or by the loss of water from the vacuole. Either process destroys the 
balance on which turgidity depends. 

Factors Enabling the Root to Exploit the Soil. — Several factors cooperate in 
enabling the plant to exploit the moisture content of the soil. The root hairs are 
continuously formed anew at a certain distance from the tip of the growing root 
so that a new supply is produced as fast as the older root hairs die. As these 
extend into untouched portions of the soil, the roots are continually pushing into 



THE INTAKE AND UTILIZATION OF WATER 21 

new soil throughout the growing season, leaving those regions from which they 
have already drawn their water and nutrient supply. 

Furthermore, the absorbing capacity of the root hairs is not limited to that 
portion of the soil with which they come in immediate contact. As the root 
hair withdraws moisture from the water films about the soil particles, these films 
become thinner than those about neighboring soil particles. Since surface 
tension maintains an equilibrium between the amounts of water on contiguous 
surfaces, water tends to distribute itself evenly. As a result it flows toward 
those parts of the soil from which water has been withdrawn, hence, in the 
direction of the root hairs. In this way the individual root hair is capable of 
absorbing water which is a considerable distance away from it. 

The movement of the roots, which their growth in length brings about, is 
likewise a movement in a definite direction, for the root tip is sensitive to differ- 
ences in the amount of moisture present on opposite sides and responds to this 
difference by bending toward that side where there is more moisture. 67 By this 
means roots grow toward those portions of the soil which have the optimum 
water content. 

Adaptation of Roots to Moisture Conditions.— In addition to the factors 
already discussed the adaptability of the root system to the condition of the 
soil is important in enabling the plant to obtain a maximum supply of water. 
A small water content of the soil, within certain limits, stimulates the roots to 
greater development, resulting in a greatly increased absorbing surface. In 
spite of this greater surface, however, the supply of water is often restricted 
and the portion of the plant above ground is not capable of much development. 
In one investigation the ratio of roots to tops for oats, grown in dry soil, was found 
to be 1:7.4 and in wet soil 1: 16.16. 126 In this second instance the roots 
remained small because the optimum conditions for moisture were exceeded. 
These figures give some indication of the correlation which exists between root 
and shoot development though the relation may be quite different in other 
plants and under other conditions. The accommodation of roots to soil con- 
ditions varies with different species. Thus Weaver 131 finds that 7 out of 10 species 
investigated by him respond to changed environmental conditions. Pulling 103 
states that characteristically shallow rooted plants such as Picea Mariana, 
Larix laricina and Betula alba papyrifera, as well as the more deeply rooted 
Pinus Strobus and P. Banksiana do not adapt themselves, while the shallow 
rooted Picea canadensis and the deeply rooted Populus balsamifera exhibit con- 
siderable plasticity. In another place the root distribution of orchard trees is 
discussed in greater detail and some of its relations to water supply are mentioned 
in that connection. 

Factors Influencing Rate of Absorption. — The ability of plants to 
absorb water depends upon the absorbing surface of their roots and on 
the following external factors: the power of the soil to deliver water, the 
temperature and aeration of the soil, its chemical properties and the 
concentration of the soil solution. Other things being equal the higher 
the temperature the greater the absorption until a certain optimum value 
is reached; temperatures above this optimum retard water absorption. 



22 FUNDAMENTALS OF FRUIT PRODUCTION 

Though water absorption is greatly reduced at low temperatures many 
plants are able to take up water when the soil temperature is below 0°C, 
for even at —3 or — 4°C, much of the soil water is not frozen and the soil 
is still capable of delivering water to the root surface. 82 

The amount of oxygen in the soil air has a marked effect on root 
absorption; if for any reason the supply of oxygen is inadequate, absorp- 
tion ceases. It should be remembered, however, that oxygen dissolved 
in the soil water is available to the root system. In fact, the oxygen 
absorbed by the living cells of the root must be dissolved in water before 
it can be taken up. The susceptibility of the roots to differences in the 
oxygen supply varies markedly with different plants. Thus roots of 
Coleus Blumei and Heliotropium peruvianum showed injury after three 
days' exposure to a soil atmosphere mixed with 25 per cent, nitrogen 
gas, while roots of Salix sp. grew freely in pure nitrogen. 32 There is some 
indication that roots of deeper penetration are less responsive to changes 
in aeration and temperature than the more superficial roots. 

The effect upon top growth of reduced absorption by the roots occasioned 
by poor aeration incident to a condition of the soil approaching saturation, is 
strikingly illustrated by the behavior of established trees of certain kinds in 
portions of India. Howard and Howard 71 record that these trees naturally 
have a short resting period during midwinter, a period often accompanied or 
preceded by leaf fall. With a rise in temperature during February, new leaves, 
shoots and flowers are formed and rapid growth continues until hot weather 
checks it. A second period of rapid vegetative growth is inaugurated with the 
advent of the monsoon, but when the soil approaches saturation, growth slows 
down again or nearly ceases. There is a third period of vegetative activity at 
the and of the monsoon when, with the drying out of the soil, the attendant 
aeration makes increased root activity possible. This third period of growth is 
finally checked by the low temperature of the winter season. 

Transpiration (and hence absorption) is decreased by the addition of small 
amounts of tartaric, oxalic, nitric, or carbonic acid to the soil and is increased 
by alkalies, such as potash, soda, or ammonia, though under field conditions 
these factors are apt to be of minor importance. 29 An increase in the concen- 
tration of the soil solution likewise decreases water absorption by its effect on 
the osmotic process. Such effects probably vary greatly with different plants. 

Submergence and Root Killing. — The effects of submergence on decidu- 
ous fruit plants are due primarily to the diminished aeration of the roots 
which this ordinarily involves. It has been found that certain land plants 
with submerged roots absorb water more rapidly at first but that later 
the rate of absorption falls off to a marked degree, the plants wilt and 
after a few days the leaves become yellow and drop. 15 After prolonged 
submergence the roots below the surface die and no new roots develop; 
eventually the entire plant succumbs. All of these effects, however, 
were alleviated or eliminated when the roots were submerged in aerated 



THE INTAKE AND UTILIZATION OF WATER 23 

water. Under these conditions some plants have survived submergence 
for three weeks. The roots lived in this aerated water but grew more 
slowly and in some cases root hairs developed. Even the roots of the 
cocoanut, though often found in a practically saturated soil, are sensitive 
to a lack of aeration, for they thrive only if the water bathing them is 
continually moving and they die if it is stagnant. 1 It is not the water 
but the lack of air in standing water that is harmful. The submergence 
to which the roots of orchard trees are occasionally subject in certain 
locations is of a type that is generally accompanied by a lack of aeration. 
The result is a prompt killing of the root hairs, followed more or less 
closely by the death of the roots themselves. This is likely to be the 
case when roots are submerged by the rise of the ground water in irrigated 
sections and in orchards planted in low-lying poorly drained ground. It 
is not so apt to be the case with trees planted on low but well drained 
bottom lands, or alluvial soils subject to occasional overflow of short 
duration during periods of flood. Even in the latter instance, however, 
it is noteworthy that the trees are apt to be severely injured, or killed, 
if the roots are submerged for more than several da}^s during the growing 
season or for a period of as many weeks during their dormant season. 
Certain bog plants like the swamp blueberry and cranberry, however, 
will stand complete submergence of their root systems for a period of four 
of five months during the winter, though submergence of as many days 
during the growing season is attended with great risk. 37 There is good 
reason to believe that many of the troubles variously attributed to 
winter injury, drought and soil infertility may be end products of tempo- 
rary root submergence that leads immediately to a kind of root pruning. 
It should be realized that root systems may be submerged though no 
water stands on the surface of the soil. More attention is devoted to this 
phase of the subject in a later chapter of this section and in the section 
on Temperature Relations. 

TRANSPIRATION 

Large quantities of water are lost by evaporation from the portions 
of the plant above ground and particular^ from the leaves. Duggar 43 
estimates that an apple tree 30 years old might lose 250 pounds of water 
a day or possibly 36,000 pounds a season. At this rate an acre of 40 
trees would represent a water elimination of 600 tons a year. This 
water loss from plants is not strictly a physical process of evaporation, 
because it is influenced by factors such as light and is subject to some 
degree of modification by the plant. Since evaporation is not affected 
in the same way by these factors the water loss of plants must be con- 
sidered a physiological process; hence it is designated transpiration. 
Whether transpiration performs any useful role in aiding the process 
of absorption of mineral constituents, or in lowering the temperature 



24 



FUNDAMENTALS OF FRUIT PRODUCTION 



of the leaves is an open question. The generally accepted opinion is 
that transpiration is a necessary evil rather than an advantage to the 
plant. 

Cuticular and Stomatal Transpiration Compared. — Transpiration is 
of two kinds; a small amount of water is lost from the cuticular surface 
of the leaf, but by far the greater proportion is lost through the stomata. 
Some measure of the proportion between these is furnished by the data 
presented in Table 13. 



Table 13. — Relation Between Stomatal Distribution and Transpiration 





Stomata per square millimeter 


Water transpired in 24 hours from 
20 square centimeters 




Upper surface 


Lower surface 


Upper surface 
(grams) 


Lower surface 
(grams) 


Pear 

Apple 









253 

246 

145 

25 

60 


5 
20 




Red currant 


35 


Linden 


49 



The amount of cuticular transpiration is relatively constant while the amount 
of stomatal transpiration can be regulated by the activity of the stomatal guard 
cells. In sunlight these cells manufacture sugars by means of the chloroplasts 
which they contain and thereby increase their osmotic concentration so that they 
absorb water from the surrounding tissue and increase in turgidity. The walls 
of the guard cells are peculiarly thickened so that when the cells are turgid, the 
stomatal aperture is open and when turgidity is lost the aperture is closed. The 
guard cells are likewise sensitive to light stimuli, to which they respond by changes 
in turgidity more rapid than those produced in the manner just described. 

The water- lost by transpiration from the leaves first evaporates from the 
surface of the mesophyll cells in the interior and collects as water vapor in the 
intercellular spaces. This water vapor then passes from the intercellular spaces 
of the leaf through the stomatal apertures to the outside. This is largely a 
process of diffusion and follows Brown and Escombe's Law which states that 
diffusion through an aperture is proportional to the radius and not to the area of 
the aperture. Thus the diffusion which might take place through 10 small 
apertures with a radius of 1 millimeter, would be equal to the diffusion which 
could take place through one aperture with a radius of 1 centimeter.- It is 
evident that if the apertures are sufficiently small and are scattered over a surface 
in such a way that the diffusion through one does not interfere with that through 
another, then diffusion through such a perforated surface will take place as if no 
surface were present. When the apertures are distributed over a surface so that 
they are about 10 diameters distant from one another, the maximum amount of 
diffusion is possible. This proportion holds roughly for the distribution of the 
stomata in most leaves. It is evident that when the stomata are opened the 
surface of the leaf offers little or no resistance to the diffusion of water vapor, 



THE INTAKE AND UTILIZATION OF WATER 



25 



but that when the stomata are closed transpiration practically ceases except for 
cuticular water loss. 

Variability in Number of Stomata in Accordance with External Condi- 
tions. — The number of stomata on the leaf surface is not determined 
in the unopened bud, but varies with the conditions under which the 
leaf develops. 

Table 14 presents data showing the reduction in the number of stomata 
per square millimeter when the available water supply in the soil is reduced. 
Though the reduction in the number of stomata per unit of leaf surface 
is not exactly proportional to the reduction in soil moisture, there is a very 
material decrease, indicating a marked ability on the part of the plant to adjust 
itself to its water supply. This flexibility is perhaps one of the reasons why 
many plants are able to thrive under wide ranges of soil moisture and atmospheric 
humidity. 

Table 14. — The Influence of Soil Moisture Upon Number of Stomata 

(After Duggar iZ ) 



Percentage of water 


Stomata per square millimeter 


in sand 


Corn 


Wheat 


38 
30 
20 
15 
11 


181 
130 
129 
124 
107 


103 

85 
82 
81 
59 



However, the number of stomata cannot be modified after the leaf 
once attains full size. This means that its ability to adapt itself 
in this way to extremes of soil or atmospheric moisture must be exercised 
early in the season. Foilage developing in the spring on a plant in a 
moisture laden soil will probably transpire somewhat more per unit of 
area later in the season, than it would had it developed under drier 
conditions, though the increase will probably not be proportional to 
the increase in number of stomata. However, the extra amount of water 
required by such plants during the summer is due mainly to the in- 
creased leaf area. If trees are so handled early in the season as to develop 
large water requirements the cultivator should recognize the fact that 
this demand will be more or less continuous through the summer and 
shape his cultural practices accordingly. 

Factors Influencing Rate of Transpiration. — The rate of transpiration 
is influenced by a number of factors, such as the character of the 
cuticle, the age of the leaf, defoliation, wind velocity, light and tempera- 
ture. 



26 FUNDAMENTALS OF FRUIT PRODUCTION 

Character of Cuticle. — The cuticular water loss of plants is affected materially 
by the thickness and character of the cuticle. The presence of a waxy coating 
diminishes the amount of water loss. The effectiveness of such a coating may be 
seen from data given by Boussingault 16 which show that an apple loses 0.05 
grams of water per cubic centimeter per hour through its cuticle, but that when 
the cuticle is removed it loses 0.277 grams or 55 times as much from the same 
surface. Cork is also an effective protection against water loss. A peeled 
potato loses water 64 times as rapidly as an unpeeled potato. 108 

Age of Leaf. — The amount of transpiration from a leaf likewise varies with 
age. The youngest leaves transpire most for the cuticle is thin and permeable; 
as the leaf grows older the cuticle thickens and permeability decreases, and with 
it the rate of transpiration. Later this rate rises to a second maximum, lower 
than the first, as the result of the development and functioning of the stomata. 
Then as the leaf ages further there is another decline in the rate of transpiration 
due possibly to changes in the properties of the epidermis. 

Defoliation. Summer Pruning. — Data presented in Table 15 show 
that the rate of transpiration is also affected by defoliation. This indi- 
cates that, though midsummer or late summer pruning to protect a 
plant and its fruit from drought injury will reduce its water requirements 
somewhat, the reduction will not be directly proportional to the percent- 
age of the foliage that is removed. 

Table 15. — The Influence of Defoliation Upon Rate of Transpiration in a 

5-year Old Fir Tree 
{After Hartig 56 ) 

Percentage Evaporation per Square Meter of 

or Foliage Surface (Grams) 

100 270 

60 272 

30 460 

10 607 

Wind Velocity. Windbreaks. — The agencies thus far mentioned as 
affecting rate of transpiration have been internal to the plant. Various 
external factors also have their effects. The most important of these 
external factors are atmospheric humidity, wind, light and temperature, 
which together determine the evaporating power of the air. It has been 
found that the rate of water loss is a simple linear function of the evapo- 
rating power of the air and that the leaf gives off water as if the water 
were at a temperature about 1°C. higher than the surrounding air. 40 

Water loss in wind is greater than in still air. This is brought out 
by the data presented in Table 16. Attention has been called already to 
the fact that one of the functions of the windbreak is to reduce the water 
requirement of the plants in its shelter. Probably the decrease in the 
amount of water required for a given unit of dry matter is not directly 
proportional to the lessened rate of transpiration consequent upon de- 



THE INTAKE AND UTILIZATION OF WATER 



27 



creased wind velocity, but in both cases the saving of water is great 
enough to be of real importance in plant production. 

Table 16. — The Influence of Wind Velocity Upon Rate of Transpiration 

(After Eberdt") 



Wind velocity 

(miles per 

second) 


Evaporation in 5 minutes from free-moving 

sunflower leaf at constant temperature and 

humidity 


Check in still air 


Before (Grams) 


After (Grams) 


2 
3 
5 


0.593 
0.631 
0.638 


0.371 
0.358 
0.361 


0.311 
0.320 
0.319 



Light. — In its lower ranges increased illumination has been found to cause 
increased transpiration irrespective of the action of the guard cells already 
discussed. 40 The effect of light may be due to absorption of radiant energy or to 
increased permeability of the membranes. The heat set free by chemical proc- 
esses or received by radiation may pass directly into the latent form without 
effecting a rise in the tempeature of the leaf: that is, it may be used completely 
in vaporizing water. Protoplasmic membranes are more permeable in light 
than in darkness and the same seems to hold for the non-cutinized cell wall. 84 

This increased rate of transpiration produced by exposure to light probably 
accounts for the characteristic action of illumination in retarding the rate of 
growth and the dependence of green plants upon light for the differentiation of 
tissues. 100 The gradual reduction in the osmotic concentration of the stomatal 
guard cells found by Wiggins 137 may also be attributed to increased permeability 
after exposure to light. In the afternoon the manufacture of soluble carbohy- 
drates is apparently more than offset by the increased permeability. Hence, 
the osmotically active substances in the guard cells diffuse into the adjoining 
cells, the guard cells lose their turgidity and the stomata close soon after dark- 
ness sets in. 

Temperature. Slope of Ground. — The rate of transpiration increases 
with rising temperature. It is one of the reasons, though probably not 
the main reason, why north slopes may be preferable to south slopes 
when moisture is a limiting factor. It likewise furnishes the explanation 
of most of the phenomena connected with the temporary wilting and later 
recovery of turgidity in plants. Of particular interest is the effect of 
temperatures below 0°C. on the transpiration from twigs. The data 
presented in Table 17 on the transpiration from a branch of Taxus baccata 
from which the leaves had been removed are interesting not only in show- 
ing the influence upon transpiration of an increase in temperature, but 
also in showing that transpiration takes place at temperatures consider- 
ably below the freezing point. Water loss under these conditions is 
associated with certain types of winter injury, a matter discussed in 
more detail in another section. 



28 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 17. — The Influence of Temperature Upon Rate of Transpiration 

(After Burgerstein 28 ) 

Water Transpired per Hour (in Per Cent. 
Average Temperature (Centigrade) op Weight op Branch) 

- 2.0 0.288 

- 2.8 0.227 

- 5.2 0.131 

- 5.7 0.127 

- 6.2 0.093 

- 6.8 0.028 
-10.7 0.019 



THE WATER CONDUCTING SYSTEM OF THE TREE 

The conduction of water from the roots to the leaves has been investigated 
by Dixon, 42 from whom the following account is largely taken. The water 
absorbed by the root hairs passes by osmosis from cell to cell through the cortex 
of the root and into the cavities of the wood cells. It then passes through the 
younger layers of wood from the roots through the trunk to the branches and 
eventually to the tracheae of the leaf. From these cells it is abstracted by the 
endodermis and eventually finds its way by osmosis to the mesophyll cells from 
whose outer surfaces it evaporates. Water passes into the cavities of the wood 
cells in the root by osmosis. The osmotic system involved here consists of the 
water of the soil, the solution in the elements of the wood, and the cortical cells 
of the roots which constitute the semi-permeable membrane separating these 
two solutions. These cortical cells have a higher osmotic pressure than the 
trachea? but, being fully distended, they function merely as a complex membrane 
across which a flow of water takes place. The concentration of the solution 
which fills the tracheae is higher than that of the soil solution and is maintained 
by the secretion of sugars from the wood parenchyma cells with which they come 
in contact. 4 This osmotic system may develop considerable pressure and result 
in the exudation of liquid from cut surfaces as in the well known phenomenon 
of bleeding in the vine. 

After the water has entered the wood cells in the root, it is carried up in the 
woody tissue in an unbroken column, which extends into the veinlets of the 
leaf. The water in the conducting tracts of high trees hangs there by virtue of 
cohesion. It must not enclose bubbles, which would break the column of 
water and permanently interfere with conduction. The structure of woody 
tissue may be considered a special adaptation which confers stability on the 
transpiration stream and prevents bubbles which may develop from occupying 
more than an infinitesimal part of the cross section of the whole water current. 
The imbibitional properties of the walls of neighboring water-filled tracheae 
render the water continuous between them. If a bubble develops anywhere in 
the transpiration stream it will enlarge until it fills the cavity of the cell in which 
it originated, but the walls of the tracheae limit the bubble and prevent its further 
expansion. From these considerations it follows that the column of water 
will not be broken unless a very large number of the conducting tubes contain 
air. Despite its mobility the water, as it rises in the wood, behaves very much 
like a rigid body. 



THE INTAKE AND UTILIZATION OF WATER 29 

The vessels may be considered as the path of the most rapid portion of the 
transpiration stream. The tracheids transmit water more slowly but continue 
to function when the water supply is limited. Though the internal thickenings 
on the walls of the trachese are essential for the transmission and stability of a 
stream under tension, the whole wall is not uniformly thickened because the per- 
meability of the thinner portions is necessary. The flow of water is further 
facilitated by the presence of bordered pits, which are themselves remarkably 
adapted to permit a flow of water under proper conditions and to prevent the 
expansion of bubbles beyond the limits of a single cell. The membrane and torus 
of each bordered pit is able to take up three positions, a median position when 
it is not acted upon by lateral forces and two lateral positions when the membrane 
is deflected against one dome or the other. When adjacent cells are filled with 
water, the membrane assumes the median position and permits a flow of water 
through the delicate membrane which surrounds the torus. When a bubble 
develops in the trachea and gradually distends until it fills it, the membranes of 
the pits in the walls of the trachea become deflected away from the bubble, until 
the torus lies over the perforation in the dome like a valve in its seat. In this 
position the tension of the water on the one side and the pressure of the gas on 
the other are withstood. 

The water after it reaches the tracheae of the leaf is drawn into the leaf cells 
by osmosis. Thus the entire transpiration stream is raised by the activity of the 
leaf cells. According to Dixon 42 these cells actually secrete the water and it is 
removed by evaporation from their outer surfaces. The resistance encountered 
by the current of water in passing through the wood at the velocity of the trans- 
piration stream is probably equivalent to a head of water equal in length to the 
wood traversed. Hence, the tension needed to raise the transpiration stream 
in a tree must equal the pressure of a head of water twice as high as the tree. 
In a tree 100 meters high, for example, a tension of 20 atmospheres is needed. 
Dixon finds the cohesion of sap to be at least 200 atmospheres, so that it is in no 
way taxed by the tension. He also finds that the osmotic concentration of the 
mesophyll cells is adequate to resist the transpiration tension and is in many 
cases much in excess of that required. Finally, he shows that the energy set 
free by respiration in the leaves is sufficient to do the work of secretion against 
the resistance of the transpiration stream. 

Summary. — The total system of water absorption, conduction and 
transpiration is more or less a unit. As a rule water is absorbed only to 
replace water lost by transpiration and in the long run the amounts of 
each are equal. For short periods, however, transpiration may slightly 
exceed absorption. The chief factors determining the flow of water 
through the plant are the available water supply and transpiration. If 
for any reason more water is transpired than is absorbed and this condi- 
tion continues for any length of time, the cells lose their turgidity and the 
plant wilts. If the supply of water is renewed in time, the plant recovers 
its turgidity without ill effects, but prolonged wilting is attended by 
serious disturbances and eventually results in death. 

Nursery stock loses its water-absorbing organs, the root hairs, upon 



30 FUNDAMENTALS OF FRUIT PRODUCTION 

digging and should be so handled until permanently planted that the 
buds cannot start. Plants in leaf should be moved with a "ball of 
earth." In most deciduous fruits aeration of soil is necessary for 
absorption and continued submergence leads to the death of root hairs 
and roots. Plants developing in the spring under circumstances such 
that they have large water requirements, continue to demand large 
amounts throughout the season and cultural operations should be shaped 
accordingly. Summer pruning may reduce water requirements some- 
what, but the reduction is not proportional to the loss of foliage. Some 
protection against water loss may be afforded by windbreaks and the 
choice of northern slopes. 



CHAPTER III 

ORCHARD SOIL MANAGEMENT METHODS AND MOISTURE 

CONSERVATION 

Most cultural practices which involve the orchard soil are for the 
purpose of influencing more or less directly its moisture supply or its 
productivity. It is well, therefore, at this point to examine somewhat 
carefully into the ways in which the several cultural practices commonly 
employed in the fruit plantation affect the water content of its soil, 
for though they must be considered also as they influence soil chemistry, 
they concern water supply even more directly. In general farm practice, 
certain soil treatments are given with the purpose of reducing, at least 
temporarily, the water content of the soil. In the orchard, however, 
excess moisture is taken care of by surface run-off and by natural or 
artificial underdrainage if the orchard has been well located. The 
efficiency of orchard soil management methods, therefore, is to be judged 
by the way in which they conserve moisture rather than by the way in 
which they dissipate it, though in some sections there may be occasion 
to dry out the soil in the fall for the purpose of hastening maturity. 

Orchard Soil Management Methods Defined and Described. — 
The commonly recognized and more or less distinct methods of soil 
management in the orchard may be listed as follows: (1) clean culture, 
(2) clean culture with cover crop, (3) artificial mulch, (4) sod mulch, 
(5) sod, (6) intercropping. There are almost endless combinations 
and forms of treatments intermediate between any two of these methods; 
consequently it is nearly impossible to differentiate clearly between them. 
For instance, clean cultivation may be practiced in the orchard until 
the first of August. If the land remains fairly clean and free from weed 
growth during the fall and winter months, the orchard is said to be 
under the clean culture method of management. If no cover crop were 
seeded, but a heavy growth of weeds comes in and serves as a fall and 
winter cover, the orchard is practically under a cover crop method of 
management, though many growers would refer to it as a clean culture 
orchard. Similarly, if the land were seeded down to bluegrass or alfalfa 
or some other forage crop, the method of soil management would be 
classed as sod, sod mulch or intercrop, depending upon what disposition 
is made of the vegetation produced between the trees. If the vegetation 
were cut and removed from the land, the orchard would be said to be 
under an intercrop system of management, but if it were pastured off 
by sheep the management probably would be called a sod system, though 

31 



32 FUNDAMENTALS OF FRUIT PRODUCTION 

if the vegetation were cut and allowed to remain on the ground as a 
mulch the treatment would be called a sod-mulch system. No attempt 
is made here to go into any detail regarding some of these systems of 
soil management that are very much alike or that are intermediate in 
character between those that stand out clearly as types. However, it 
is desirable to recognize how certain of the typical systems of soil manage- 
ment may be expected to influence the water content of the soil and, 
through it, the growth and behavior of the tree. With this information 
at hand, it will not be difficult, as a rule, to predict more or less accurately 
the results that may be expected from one of the intermediate or combi- 
nation treatments. 

Orchard -soil Management Methods and Surface Run -off. — A 
word may be said first regarding the influence of these several methods 
of soil treatment upon surface run-off. Much of course depends upon 
the lay of the land, the character of the soil itself and the way in which 
precipitation occurs. Most soils cannot take up the water that falls 
in a torrential rain lasting but an hour so completely as they can the same 
amount of rainfall distributed over a 12- or 24-hour period. Exact 
figures are not available, but it has been observed many times that there 
is much less run-off from sodded areas than from equal areas of similarly 
lying bare land. The covering of vegetation or of mulching material 
checks the flow of the water over the surface of the ground and gives 
it a greater opportunity to soak in. Furthermore, if there is any con- 
siderable amount of mulching on the ground it acts as a sponge, first 
absorbing the water as it falls and then permitting it slowly to seep into 
the soil. In this connection, mention should be made of the influence 
of mulching material or vegetation of any kind upon erosion. There 
are many orchards and parts of many others, planted on slopes so steep 
that there would be much loss of soil from washing, were the land to be 
cultivated and left bare any considerable portion of the year. Orchards 
of this type should be left in sod or artificially mulched, regardless of 
how these treatments may influence the water or nutrient supply avail- 
able to the trees. 

Moisture Under Tillage and Sod-mulch Systems of Management. — 
There is little reason to believe that there is much difference between, 
the methods of soil management in the amounts of seepage into the lower 
layers of the soil. However, it is obvious that these several treatments 
would have very different influences upon surface evaporation from the 
soil and the evaporation that takes place through the plant itself. Fortu- 
nately, considerable data are available upon certain phases of this 
question. 

Some New York and Pennsylvania Records. — The New York data 
presented in Table 18 show nearly 5 per cent, difference in soil moisture 
between the surface soils of the tilled and of the sodded orchards and 



ORCHARD SOIL MANAGEMENT METHODS 



33 



nearly 4 per cent, difference in the respective subsoils. When it is con- 
sidered that a part of the water in each case is unavailable for tree growth 
because needed to supply the hygroscopic requirements of the soil, it is 
evident that the tilled ground may contain many times as much available 
moisture as the land in sod and that the difference between the two 
methods of culture in respect to the available water is actually much 
greater than the figures would suggest at first glance. The Pennsylvania 
data presented in Table 19 show clearly that artificial mulching may be 
and indeed usually is, a most efficient means of reducing evaporation. 
They also throw some light on the effect of intercrops and cover crops 
upon the water content of the soil, though no information is available as 
to the season in which the determinations were made. Incidentally, 
Table 19 shows how the soil-water supply influences the growth and the 
yield of apple trees, though it should not be inferred that all the differences 
in growth and yield are due directly to the variations in water supply. 
It is significant, however, that there is a close correlation between the two. 



Table 18. — Soil-moisture Determinations in a Mature Apple Orchard in 

New York 69 
(Under different methods of soil management) 



1907 


1908 




1 to 6 inches 


6 to 12 


inches 


Date 


1 to 6 inches 


6 to 12 inches 


Date 


Till- 
age 


Sod 


Till- 
age 


Sod 


Till- 
age 


Sod 


Till- 
age 


Sod 


6-28 


12.71 


6.23 


12.90 


6.31 


7- 7 


12.77 


11.59 


11.56 


10.70 


7- 2 


14.88 


11.20 


14.86 


6.99 


7-10 


12.43 


6.62 


10.89 


6.29 


7- 5 


12.07 


5.87 


10.96 


3.37 


7-14 


12.69 


9.00 


10.58 


6.03 


7- 9 


13.12 


6.96 


12.04 


6.53 


7-22 


18.31 


14.02 


17.76 


9.59 


7-12 


16.43 


13.51 


15.31 


9.26 


7-24 


15.25 


11.85 


16.14 


9.37 


7-16 


13.77 


9.63 


11.75 


8.69 


7-28 


12.40 


10.84 


11.67 


8.25 


7-19 


11.68 


9.51 


9.48 


7.80 


7-31 


15.50 


13.31 


15.56 


10.09 


7-23 


13 42 


8.36 


9.19 


7.80 


8- 4 


14.00 


12.97 


12.84 


10.87 


7-26 


11.93 


6.81 


8.84 


5.21 


8- 7 


15.35 


9.72 


15.31 


7.61 


7-30 


11.69 


5.46 


9.84 


4.72 


8-11 


15.27 


10.08 


15.28 


8.02 


8- 2 


13.20 


7.82 


10.92 


5.75 


8-14 


14.72 


11.70 


12.47 


8.10 


8- 6 


10.64 


7.08 


10.72 


5.47 


8-18 


14.56 


14.07 


12.98 


12.71 


8- 8 


10.02 


4.82 


10.15 


3.80 


8-21 


12.33 


8.70 


11.21 


7.81 


8-14 


11.79 


4.38 


9.62 


4.07 


8-25 


10.98 


6.39 


9.39 


6.08 


8-17 


9.37 


5.21 


9.07 


3.58 












8-20 


8.56 


3.99 


8.18 


2.68 












Average for 


12.20 


7.30 


10.86 


5.75 




14 04 


10.06 


13.12 


8.68 



34 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 19. — Influence of Cultural Methods on Moisture, Growth and Yield 

in a Young Orchard 
(Results from Experiment 331, first 7 years, 1908-1914 122 ) 



Treatment 



Moist- 


Rela- 




ure 


tion to 


Average 


content 


optimum 


gain in 


1913, 


content, 


girth, 


per 


per 


inches 


cent. 


cent. 





Gain 
over 
tillage, 
per 
cent. 



Total 

yield 

1914, 

pounds 



General 
rank 



Tillage 

Tillage and intercrop .... 
Tillage and cover crop . . 
Cover crop and manure. 
Cover crop and fertilizer 

Mulch 

Mulch and manure 

Mulch and fertilizer. . . . 



10.6 

5.5 

8.5 

9.2 

9.4 

17.1 

18.2 

18.1 



53.0 


6.84 


27.6 


7.69 


42.7 


6.84 


45.9 


8.31 


47.2 


7.76 


85.6 


8.29 


90.8 


8.76 


90.4 


8.93 



12.4 

21.5 
13.5 
21.2 
28.1 
30.5 



1 


5 


21 


6 


7 





135 


4 


18 


9 


38 


5 


300 


5 


390 


1 



Some New Hampshire Records. — That the moisture supply in a tilled 
orchard is not invariably superior to that in one under a sod-mulch system 
of soil management is shown by the data presented in Table 20 from an 
orchard on light sandy loam in New Hampshire. In this instance 
measurements were taken of the percentage of moisture in the surface 
7 to 9 inches of soil and in the subsoil (to a depth of 3 feet) at weekly 
intervals during the growing periods of four successive seasons. The 
figures represent seasonal averages. 

Gourley, in reporting these observations, suggests that the lower moisture 
in the tilled plot may be due in part to the greater permeability of the subsoil 
and in part to the absence of a covering to shade the soil. Additional factors 
cited as possible explanations are a slight mulch in the sod plot, the slight demand 
made by the poor grass and finally, the increased drain on the soil in the tilled 
plot due to the larger growth and larger leaves on the apple trees growing there. 
It should be stated that despite the higher moisture content in the sod plot the 
growth and yields there were inferior. Gourley, discussing a late summer 
drought accompanied by a severe dropping of fruit, states, "The dropping was 
just as severe in the heavier soil which showed 12 per cent, of moisture as in the 
lighter soil which showed about 7 per cent, which would agree with the findings 
of the soil physicists on the wilting point in light and heavy soils." 

English Experience. — Bedford and Pickering 14 report some interesting data 
showing that uniform results are not attendant upon similar treatments. "Pot 
experiments under glass indicated that, during the summer months, 30 per cent, 
more water was lost from the pots where there was a surface crop than from those 
where there was none; but when the pots were in the open, exposed to the sun 
and wind, the reverse was often — not always — the case, and the evaporation 
from the pots with the surface crop might, during the season, be even less than 
half of that from those without a surface crop." 



ORCHARD SOIL MANAGEMENT METHODS 



35 



Table 20. — Moisture Determinations on Sod Cultivation and Cover Crop 

Plots 

(Light sandy loam in New Hampshire) 

(After Gourleif 2 ) 

Surface soil 



Year 


Sod 


Tillage 


Tillage and cover 
crops 


1913 
1914 
1915 
1916 


16.02 

18.87 
25.63 
20.48 

20.25 


13.69 
13.39 
19.29 
16 . 45 


14.20 
15.03 
20.82 
21.31 


Average 


15.70 


17.84 




Sub 


soil 




Year 


Sod 


Tillage 


Tillage and cover 
crops 


1913 
1914 
1915 
1916 


10.98 
14.14 
14.26 
14.82 


9.06 

9.78 

14.03 

12.74 


8.93 
10.26 
13.33 
13.24 


Average 


13.55 


11.40 


11.44 



At Harpenden they found during May, June and July an average of 4 per 
cent, more moisture in tilled soil than in grass land; in Ridgmont soil, grassed 
land in August and September contained on the average 0.7 per cent, more water 
than tilled land. In no case did the amount of moisture appear to be the chief 
factor in tree growth. Irrigation increased the vigor of fruit trees growing in 
grass land, but did not make them as thrifty as those grown in tilled ground. 



The New Hampshire and the English results agree in the superior 
growth made by trees in tilled ground, despite the absence of significant 
differences in moisture, or indeed, despite the frequent superiority of 
grass land in moisture content. In these cases there is evidence of the 
effect of other limiting factors, some of which are discussed in the section 
on nutrition. 

Special cases deserve passing consideration. The Hitchings orchard 
in New York showed under test as good results in growth and yield under 
the sod-mulch system as under tillage. 60 This condition is explained as 



36 FUNDAMENTALS OF FRUIT PRODUCTION 

the result of seepage from the hill at the bottom of which the orchard is 
located, supplying so much water that moisture is eliminated as a limiting 
factor. Many orchards in the eastern United States are in just such 
locations. 

Some Kentucky and Kansas Records. — Some of the findings of the 
United States Bureau of Soils on soil moisture conditions in grass land 
and in cultivated soil may be summarized here. Records were made 
during the months of May, June and July, 1895, of the water content of 
soils at a number of places in the United States and under different 
tillage conditions. 128 These records bring out a great difference between 
soils in the way this moisture content is influenced by treatment. For 
instance, at Greendale, Ky., during the last half of May, the moisture 
contents of uncultivated, bare land and of bluegrass sod were pract- 
ically the same (about 18 per cent.) ; during June, however, the moisture 
content under the bluegrass gradually decreased to about 10 per cent, 
while that of the uncultivated bare land remained about 17 per cent, 
except for a period of about 5 days at the end of the month when it 
dropped practically to the figure shown by the sod land. During July 
the bare, uncultivated land averaged 2 to 3 per cent, higher in moisture 
content than the grass land. At Lexington, Ky., a similar series of 
records showed an average moisture content about 5 per cent, higher dur- 
ing May, 8 to 10 per cent, during June, and 1 to 5 per cent, during July, 
in the bare, uncultivated land compared with that under bluegrass sod. 
During June the bluegrass made its very heavy draft upon the moisture 
supply of the soil, lowering it to the point where little water was available 
for plant growth and cultivated crops consequently suffered. 

This suggests that if the sod-mulch system of orchard culture checks 
tree growth materially during the early part of the season or again after 
mid-season it is not on account of its lowering the water content of the 
soil, at least in those sections favored with summer rains. On the other 
hand, orchards in sections likely to have little rain between the middle 
of June and early fall probably would suffer materially from drought during 
that period. In any case, the growth of grass mulching material would 
take large amounts of water during June; during that month the itrees 
may or may not be able to spare it. The question of the practicablity, 
desirability or efficiency of the grass mulch method of culture so far as it 
concerns soil moisture therefore depends on what precipitation can be 
expected reasonably during July, August and September or what can be 
applied by irrigation — for orchards under these two methods of soil 
management are very likely to enter this period with material differences 
in the amount of available soil moisture. In Scott, Kan., on the other 
hand, the moisture content of prairie sod land has been found to average 
only about 8 per cent, during the last half of May, while cultivated land 
averaged about 17 per cent. Rains late in May and scattered through 



ORCHARD SOIL MANAGEMENT METHODS 37 

June and July, brought up the averages in both soils to well above the 
danger point for plant growth and the cultivated soil averaged only 2 to 
5 per cent, more moisture during those months. 

In General. — That the sod-mulch, or any other sod method of manage- 
ment, makes something of a draft upon the water supply of the soil, as 
compared with a tillage method of management, cannot be denied, though 
this draft is often less than is supposed. It would be a very good sod- 
mulch indeed that would produce 1 dry-weight ton of mulching material 
per acre. More frequently the amount does not exceed half that figure. 
One-half ton of dry mulching material would require from 31,250 to 
62,500 gallons of water, assuming from 250 to 500 parts of water for each 
part of dry matter. This would be the equivalent of 1)4 to 2% acre-inches 
of rainfall or irrigation. Furthermore, most of this water is used by the 
grass during the months of April, May and June, when the soil is most 
likely to be well supplied with moisture and best able to part with it. If 
the growing season of the grass is followed by moderate or heavy summer 
rains or irrigation the requirements of the trees will be well taken care of 
in this respect. On the other hand, if there should follow a period of 
drought, it is easy to understand why trees under sod treatment would 
suffer. An important factor, then, in determining the practicability of the 
sod-mulch method of management is the likelihood or certainty of summer 
precipitation, or, what amounts to the same thing, available irrigation 
supply during the summer months. In sections such as the Willamette 
valley of Oregon where winter and spring rains are abundant but the 
summer is dry, the sod-mulch method of management cannot be employed 
safely without irrigation. In such regions it is wise to use every means 
of conserving the natural water supply. On the other hand, there are 
many sections and many locations where summer rains can be counted 
on to supply the requirements of the trees during their growing season 
year after year; in other cases an orchard may be so located in a valley 
floor or a piece of bench land that it is sub-irrigated by means of seepage 
water. Under these conditions the sod-mulch method of management is 
entirely practicable, though it should be stated that such orchards may 
need somewhat different treatment, so far as nutrition is concerned, than 
orchards in cultivation. A study of the records of the United States 
Weather Bureau showing monthly precipitation over a series of years 
will give important data as to the relative desirability or practicability 
of these several methods of soil management for any particular region 
or district. 

Sometimes the choice of methods is influenced by considerations 
of the cost of the systems. Hedrick 60 reports that the operations 
involved in the sod-mulch and tillage systems cost per acre respectively: 
for the Auchter orchard 80 cents and $7.39, for the Hitchings orchard 
72 cents and $16.28. In many cases the tillage method will more than 



38 FUNDAMENTALS OF FRUIT PRODUCTION 

return the extra labor cost; however, when results are equal, costs should 
be considered. 

Practicability of the Sod-mulch System Influenced by Depth of Rooting. — 
Mention of depth of rooting, a subject considered in more detail later, 
is pertinent to this discussion. A tree with a root system penetrating 
the soil to a depth of 8 or 10 feet can draw upon the moisture supply of a 
large volume of soil. Such a tree is in a much better position to with- 
stand temporary surface drying such as may be produced by evaporation 
from the surface or from weeds and grass, than a tree whose roots are 
limited to the upper foot or eighteen inches of soil. Consequently 
it will thrive under the sod-mulch method of culture when a shallow- 
rooted tree would suffer serious injury. To keep an orchard in sod under 
conditions such that deep rooting is not possible and where there is not 
an abundant summer rainfall or plenty of irrigation water, is to invite 
trouble. However, there are successful orchards in sod where the 
summers are long and dry and irrigation is not known. The explanation 
lies in the deep root system of the trees that makes them independent, 
to a great degree, of surface soil conditions. 

In passing it should be mentioned that the grass, both cut and uncut, 
of the sod systems of management affords some protection against surface 
evaporation, the exact degree depending on the thickness of the protective 
layer. As this layer is frequently rather thin, its importance in checking 
evaporation is often exaggerated, for the stubble of the cut grass continues 
to evaporate moisture into the air, even after it has turned brown and has 
died down to the ground. In some cases this water-dissipating action 
of the stubble during the summer months may even equal the protective 
action of the mulch against evaporation. 

Influence of Depth and Frequency of Cultivation Upon Soil Moisture. 
Since cultivation is in general a means of conserving soil moisture, 
the presumption is that the deeper the cultivation, within reasonable 
limits, the more effective it will be. Table 21 affords a fairly accurate 
idea of how depth of soil mulch influences the loss of water by evaporation. 
It is worthy of note that with a soil mulch 6 inches deep the water lost 
by evaporation is less than a quarter of that lost through a 1-inch mulch. 
Regardless of the texture of the soil, cultivation is equally effective as a 
protection against water loss: this protective influence is felt to a depth 
of 6 feet. 

Table 21 is interesting also because it shows the combined effects of 
depth and frequency of cultivation. It is evident that increasing the 
frequency of the cultivations, at least up to a certain point, increased the 
effectiveness of the soil mulch under the conditions of the experiment. 
Probably under arid or semiarid conditions with few or no summer rains 
and less weed growth the more intensive tillage would not give materially 
increased protection against evaporation. 



ORCHARD SOIL MANAGEMENT METHODS 



39 



Table 21. — The Relative Effectiveness of Soil Mulches of Different Depths 
and Different Frequencies of Cultivation 78 



Depth 
of soil 
mulch, 
inches 


Loss of water per acre 
per 100 days 


Cultivation 


None 


Once in 
2 weeks 


Once per 
week 


Twice per 
week 


1 


Tons 


724.1 
6.394 

724.1 
6.394 

724.1 
6.394 


551.2 
.4.867 
23.88 

609.2 
5.380 

15.88 

612.0 
5.402 
15.49 


545.0 
4.812 
24.73 

552.1 
4.875 
23.76 

531.5 
4.694 
26.60 


527 8 


2 


Inches 

Water saved, per cent 

Tons 


4.662 
27.10 

515 4 




Inches 


4 552 


3 


Tons 


28.81 
495 




Inches 


4 371 




Water saved, per cent 


31.64 



Intercrops and the Soil Moisture Supply. — The influence of various 
intercrops upon soil moisture conditions in the young orchard has been 
studied by Emerson. 45 Results of these studies, covering two successive 
seasons, 1901 and 1902, are presented graphically in Fig. 1. These two 
seasons afforded more or less extreme conditions of precipitation. The 
summer of 1901 was characterized by very light rainfall, so light in fact 
that the trees would have to depend largely upon stored moisture during 
the period of their most active growth. On the other hand, the summer 
of 1902 was a season of abundant rainfall. The crops grown in the 
vegetable plot included water melons, bush beans, pole beans and turnips. 

In commenting upon the results of this investigation Emerson says: 
"The vegetables dried the soil but little more than clean cultivation. In 
neither case did the percentage of moisture become dangerously low, even during 
the protracted drought of 1901, when only a little over 7 inches of rain fell during 
the 4 months from May to August inclusive. The crops of rye dried the ground 
much more than any other method of culture tried. Not only was the rye ground 
somewhat drier, but it became dry earlier, and moreover, since no rains occurred 
to thoroughly moisten the ground after it had once become dry, the rye plot 
remained dry nearly a month longer than any of the other plots. Next to rye, 
the oat crop dried the soil most seriously during the dry season of 1910, though it 
did not make the soil much drier than corn or cover crops. Its effect, however, 
was noticeable much earlier in summer and lasted much longer. By the middle 
of July, when the corn plot was becoming dry, many trees have completed their 
greatest length growth and do not need so large a supply of moisture as they do 
earlier in the season. The corn plot was very dry, therefore, only about half as 
long as the oats plot. The important difference between the cover crop and the 
corn, just as between the corn and the oats, is that the soil in the cover crop plot 



40 



FUNDAMENTALS OF FRUIT PRODUCTION 



did not become dry for a week or two after the corn ground had become dry. 
The great difference, as regards soil moisture between the clean cultivation 
on the one hand and the rye and oats on the other is fully appreciated only when 
it is remembered that the moisture in excess of 8 or 10 per cent, (in this particular 
soil) is available to plants. . , , In 1902, the plots did not vary greatly as regards 




Fig. 1. — Percentages of soil moisture in orchard plots and inches of rainfall during 
summers of 1901 and 1902. The curved lines indicate the fluctuations in soil moisture 
content. The vertical bars show dates and amounts of rainfall. (After Emerson. 46 ) 

soil moisture. Naturally, no method of culture dried the ground seriously at 
any time during this very wet season, when over 28 inches of rain fell during the 
4 months from May to August inclusive." 45 

Table 22 presents data showing the effects of the various intercrops 
in this Nebraska experiment upon the drought killing of newly set trees. 



ORCHARD SOIL MANAGEMENT METHODS 



41 



Table 22. — Effect of Various Intercrops on Drought Killing of Young 

Trees (After Emerson ib ) 



Intercrop 



Apple 



Cherry 



Peach 



Num- 
ber 
set 



Num- 
ber 
died 



Per 
cent, 
died 



Num- 
ber 
set 



Num- 


Per 


Num- 


Num- 


ber 


cent. 


ber 


ber 


died 


died 


set 


died 



Per 

cent, 
died 



Watermelon crop. 
Watermelon crop. 

Corn crop 

Clean cultivation. 

Oats crop 

Cover crop, millet 
Cover crop, oats. . 
Cover crop, weeds 



30 


2 


7 


30 


2 


7 


30 


2 


7 


30 


1 


3 


30 


14 


47 


30 


4 


13 


30 


4 


13 


30 


7 


23 



12 
12 
12 
12 
12 
12 
12 
12 



9 


10 





17 


10 





9 


10 


2 





10 





50 


10 


8 


17 


10 


1 


33 


10 





50 


10 










20 



80 

10 







Table 22. — Continued 



Intercrop 



Pear 



Plum 



Total 



Num- 
ber 

set 



Num- 
ber 
died 



Per 


Num- 


Num- 


Per 


Num- 


Num- 


cent. 


ber 


ber 


cent. 


ber 


ber 


died 


set 


died 


died 


set 


died 



Per 

cent, 
died 



Watermelon crop. 
Watermelon crop. 

Corn crop 

Clean cultivation. 

Oats crop 

Cover crop, millet 
Cover crop, oats. . 
Cover crop, weeds 



10 
10 
10 
10 

10 

10 
10 
10 




20 
20 
10 
60 
20 
10 





14 


1 


7 


76 


4 


14 








76 


6 


14 








76 


7 


14 








76 


2 


14 


5 


36 


76 


39 


14 





o- 


76 


9 


14 


1 


7 


76 


10 


14 


2 


14 


76 


15 



5.4 

7.9 

9.2 

2.6 

51.3 

11.8 

12.2 

19.7 



The data for the cover crops indicate relatively more injury than would 
occur in older orchards because the cover crops probably made a much 
more vigorous growth than they would in competition with well estab- 
lished trees. The suggestion is made, however, that cover crops should 
be selected and used with considerable care in recently established 
orchards. The danger from the use of the small grains as orchard inter- 
crops is indicated plainly. On the other hand, little loss is occasioned 
by the growing of tilled or hoed intercrops. 

Cover Crops and the Moisture Supply. — Orchard cover crops are not 
generally considered in relation to soil moisture, but rather as means of 
adding organic matter to the soil and increasing productivity. Never- 
theless they do influence water content in several ways and some data on 
this question have already been presented in connection with the discus- 
sion of intercrops. As this influence is, in many cases, important it seems 
desirable that further consideration be given the matter. 



42 



FUNDAMENTALS OF FRUIT PRODUCTION 



Effects of Early and Late Seeding. — Cover crops use considerable 
water in their growth. A good cover crop probably produces at least 
x /l ton of dry matter per acre involving the transpiration of from 2 to 4 
acre-inches of water. However, the cover crop makes its demand for 
water upon the soil during the fall, winter and spring months — a time 
when there is most likelihood of an abundant water supply and conse- 
quently when the trees are not so likely to be injured by the draft of the 
cover crops. It is true that cover crops are usually seeded in late July or 
in August, but their growth is so limited before the middle or end of 
September that they compete but little with the trees for either nutrients 



Table 23. — Percentage of Soil Moistttre in Bare Ground and Under Cover 
Crops in Early November After a Drought 38 



Depth in inches 


Bare ground Hairy vetch 


Cowpea 


1 to 12 
12 to 18 
18 to 24 


6.48 
8.52 
7.60 


12.15 
10.30 
11.65 


9.30 

12.27 
9.80 



Table 24. — Percentage of Soil Moisture for Each Cover Crop from Nov. 1, 
1905, to Feb. 17, 1906, and the Average for Three Determinations 41 



Crop 



Percentage of moisture in soil to depth of 30 inches 



Nov. 
21-22, 1905 



Jan. 
2-3, 1906 



Feb. 
16-17, 1906 



Average 



Cowpeas 

Soy beans 

Crimson clover 

Hairy vetch 

Oats 

Canada peas 

Oats and Canada peas. . . 

Rye 

Check 

Millet 

Rape 

Turnip 

Turnip and rye 

Hairy vetch and Canada 

peas 

Oats and crimson clover. 
Cowpeas and crimson clover 

Average 



17.7 
18.9 
18.6 
17.4 
17.0 
17.7 
16.7 
16.5 
16.2 
16.1 
16.5 
16.3 
15.5 

17.3 
17.6 
18.1 

17.1 



24.5 
23.2 
23.7 
24.6 
22.7 
21.4 
25.5 
22.5 
22.4 
23.4 
24.0 



23.5 



21.9 
23.4 
23.4 
20.5 
21.2 
18.8 
22.0 
21.7 
20.4 
20.6 
21.7 
19.3 
22.5 

19.2 
20.0 
26.7 

21.5 



21.7 
21.9 
21.9 
20.8 
20.3 
19.3 
21.1 
20.2 
19.7 
20.0 
20.7 



20.7 



ORCHARD SOIL MANAGEMENT METHODS 43 

or water. Furthermore, the protective action of the cover crop through 
checking wind velocity close to the ground and through shading the soil, 
thus lowering its temperature, may fully compensate for its use of water 
during the late summer and early fall. The data presented in Tables 23 
and 24 show that later in the season, cover crops may actually contribute 
indirectly to the soil moisture content. The examinations recorded in 
Table 23 were made at Ithaca, N. Y., in November 1901, at the close of an 
extended drought. Those recorded in Table 24 were made at intervals 
during the winter of 1905-1906 in Wisconsin. The report upon this 
latter investigation states that the moisture determinations taken in the 
spring on the soil under these cover crops confirms the results obtained 
in the fall and winter "in that it shows the average moisture content of the 
covered ground to be considerably more than that of the bare ground." 41 
There are distinct differences between various cover crops in their influ- 
ence upon the water content of the soil. 

However, if cover crops are started so early in the season that a 
considerable amount of growth is made during July and August, or even 
early September, they are likely to make serious drafts upon the water 
supply of the surface soil, which might check the vegetative growth of the 
trees prematurely and reduce the size of the fruit. Striking evidence on 
this point is furnished by an experiment in which cylindrical cans were 
filled with heavy soil from an orange grove. 23 One was left undisturbed 
as a check, in one a surface soil mulch was maintained and one was seeded 
to barley. The experiment was started June 25, at which time the soil 
contained 19.2 per cent, moisture. At the end of 38 days the soil in the 
check cylinder contained 10.1 per cent., the mulched soil 14 per cent, and 
the soil seeded to barley 3.1 per cent, moisture. The soil seeded to barley 
had reached its wilting coefficient 21 days after seeding. 

In certain cultural experiments in Pennsylvania the beneficial effects 
of cover crops expressed in vegetative growth and yield have been most 
apparent during the moist seasons, and little or no benefit has been 
derived from their use during dry years. 123 The rapid drying effect of 
oats, when used as a cover crop for peaches in Delaware, has prevented 
"the best growth of new wood to produce the maximum number of fruit 
buds." 94 The rate of growth of cover crops as the season advances is an 
important factor in determining their draft upon the water supply of the 
soil from week to week. From this point of view, the ideal cover crop is 
one which grows slowly at first but rapidly late in the season when the 
trees do not require so much moisture and when the supply is more 
abundant. Figures on the rates of growth, under Wisconsin conditions, 
of some of the more common crops of the Northern states are given in 
Table 25. The indirect influence of cover crops upon soil moisture in 
adding organic matter to the soil and thereby increasing its water-holding 
capacity is more difficult to estimate accurately, but there is reason to 



44 



FUNDAMENTALS OF FRUIT PRODUCTION 



believe that its importance in that connection has been overemphasized 
often. 

Table 25. — Rate of Growth of Different Crops from Aug. 25 to Oct. 2 41 

(Height in inches) 



Aug. 25 



Sept. 3 



Sept. 15 



Sept. 23 Oct. 2 



Cowpeas 

Soy beans 

Crimson clover 
Hairy vetch . . . 

Oats 

Canada peas. . 

Rye 

Rape 

Turnip 

Millet 



4.5 
4.5 



5.5 
2.5 
2.5 
3.0 



10.0 
8.0 
3.0 
4.5 

11.0 
8.0 
8.0 
4.0 
4.0 
5.0 



12.0 
13.0 

3.5 

5.0 
16.0 
13.0 

9.0 
10.0 

7.0 
11.0 



14.0 

14.5 

4.0 

5.5 

18.0 

20.0 

10.0 

14.0 

8.0 

12.0 



20.0 
22.0 
6.0 
8.0 
24.0 
24.0 
12.0 
16.0 
12.0 
18.0 



Winter-killed and Winter-surviving Cover Crops. — Cover crops are 
generally classed as leguminous and non-leguminous when considered 
in relation to their influence upon soil productivity. Emerson suggests 
that when they are being considered as they influence soil moisture a 
better classification would be winter-killed and winter-surviving. 46 The 
degree of cold actually experienced in a particular section determines 
whether a given crop is killed by or survives the winter. Hence, a crop 
that belongs in the one class in one place may fall in the other in some 
other section. Any cover crop that survives the winter and resumes 
active growth draws upon the moisture supply of the soil in the spring 
and will continue to do so until plowed under or until cultivation of some 
kind is begun. Since it is generally considered inadvisable to plow or 
cultivate deeply while trees are in bloom or the fruit is setting and since 
soil moisture conditions and the press of other work often make the 
plowing of the orchard before blossoming impracticable, cultivation is often 
not begun until late in May or early in June. This gives a winter-sur- 
viving cover crop an opportunity to make considerable growth in the 
spring, often more than it was able to make the previous fall. The 
general effect of this growth upon soil moisture is shown by the figures in 
Table 26 and is presented graphically in Fig. 2. By June 3 the winter- 
surviving cover crop had reduced the soil moisture to approximately 
half the amount in the soil protected by a winter-killed crop. In fact it 
had consumed practically all the available moisture, leaving the water 
content of the soil but little above its wilting coefficient. In regions of 
comparatively high rainfall during the spring months, this water loss due 
to the growth of winter-surviving cover crops would be of secondary 
importance and it would likewise be unimportant in sections with 



ORCHARD SOIL MANAGEMENT METHODS 



45 



Table 26. — Effect of Various Cover Crops on Soil Moisture During the 

Spring of 1901 46 



Kind of crop 



Percentage of soil moisture 



Apr. 19 



Apr. 27 



May 20 



June 3 



Winter-killed crops: 

Oats 

Millet 

Cane 

Average 

Winter-surviving crops 
Rye 



28.7 
26.0 
24.0 

26.2 

22.6 



20.2 
21.8 
22.1 

21.4 

17.4 



20.5 
21.9 
21.7 

21.4 

12.2 



20.1 
20.7 
20.7 

20.5 

11.2 



abundant and cheap irrigation water, but in those sections or in 
those seasons with a light late spring and £7 
summer rainfall it could easily occasion 
much more financial loss than would be 
compensated by the advantages accruing 
from the use of the cover crops. A certain 
quantity of organic material produced in 
the autumn is just as valuable for soil 
improvement purposes as an equal amount 
grown in the spring. c 

Wind Velocity and Evaporation : Wind- c 
breaks. — Attention has been called to the £ 
almost continual evaporation of water from 
the soil. In regions of low precipitation 
this amounts to a much larger percentage 
of the total supply than in regions of fre- 
quent and abundant rains. Assuming 
uniform soil management methods, evap- 
oration may be expected to rise with an 
increase in wind velocity and to vary 
with temperature of the soil water, with 









]■§ 






Irn 






li 






t Irn 






R 






\-» 






W 




t 33 












vs. 

Vft 



































April 



June 



May 
1901 
Fig. 2. — Percentages of soil 
moisture in plots of winter-killed 
temperature of the air close to the evapO- and winter-surviving cover crops, 

rating surface, with vapor pressure in the spring of 1901. The dots show the 

. . dates of making the moisture de- 

air near the water and with atmospheric terminations and the exact percent- 
humidity. The onlv One of these factors ages of moisture found The curved 
• lines indicate the probable fluctua- 

at present Under the control of the grower tions in moisture between these 

to any considerable extent is wind velocity. dates - (After Emerson. 46 ) 
Consequently it is discussed at this time. In one series of determinations 
when the relative humidity was 50 per cent, and the air temperature 84°F. 
evaporation was found to be 2.2 times as rapid with a wind velocity of 5 



46 FUNDAMENTALS OF FRUIT PRODUCTION 

miles per hour as in a calm atmosphere; 3.8, at 10 miles per hour; 4.9, at 15 
miles per hour; 5.7 at 20 miles per hour; 6.1, at 25 miles per hour and 6.3 
at 30 miles per hour. 107 The influence of windbreaks upon wind velocity 
varies with their height and density and much depends also on the topog- 
raphy. Card 33 measured the evaporation in Nebraska at varying 
distances from the protected side of a windbreak of forest trees some 30 
feet high, during the period July 15 to Sept. 15, and for those portions of 
the period when the wind was from the south, southeast and southwest, 
these being the most drying winds. Expressing the evaporation at a 
point 300 feet south of the windbreak as 100, evaporation 200 feet north 
was 83 and 50 feet north, 55. During a 12-hour period on Aug. 3, when 
the weather was hot and dry with a high wind, evaporation 50 feet north 
of the windbreak was 29 and 200 feet north it was 67, compared with 100 
at a point 300 feet south. It is thus evident that wind barriers of one 
kind or another reduce evaporation very materially. However, the 
moisture required for the growth of the windbreak materially reduces 
their total moisture-conserving effect, though deep plowing or subsoiling 
close to the windbreak reduces its injurious influence in this direction. 

Summary. — There are six fairly distinct methods of soil management 
commonly used in the deciduous fruit plantation: (1) clean cultivation, 
(2) clean culture with cover crop, (3) artificial mulch, (4) sod mulch, 
(5) sod, (6) intercropping. The sod and sod-mulch systems are most 
effective in reducing run-off and in preventing erosion; in certain situa- 
tions their use is to be recommended for these reasons if for no other. 
The various systems of soil management employing tillage generally 
conserve a larger percentage of the water that enters the soil and conse- 
quently they are more effective in preventing injury from drought. The 
sod-mulch method has its place where abundant summer rainfall, deep 
rooting or availability of irrigation water largely removes the trees from 
competition with the surface cultures for water. The moisture-conserv- 
ing effects of tillage increase somewhat with its frequency and depth, but 
when cost is considered there is a decreasing margin of profit with the 
deeper and more frequent cultivation. Cultivated intercrops may be 
used safely in the orchard, but the small grains are apt to make too serious 
a draft on moisture at a period when the trees should be abundantly 
supplied. Cover crops consume considerable moisture but unless planted 
too early they are not likely to injure the trees seriously by their growth 
in the fall. In fact they may actually conserve moisture for the trees 
by cutting down surface evaporation and holding snow. In some sections 
winter-surviving cover crops should not be used because of their draft the 
on moisture supply in the spring when the trees require it. This is partic- 
ularly true in sections with only moderate rainfall and long dry summers. 
Evaporation increases rapidly with wind velocity and moisture losses 
from this cause can be lessened materially in many cases by choice of 
sites and use of windbreaks. 



CHAPTER IV 

SOIL MOISTURE: ITS CLASSIFICATION, MOVEMENT 
AND INFLUENCE ON ROOT DISTRIBUTION 

Within certain limits the size and general character of top growth is 
influenced by the root system that supports it. Similarly the size and 
distribution of the root system depends to an important degree on the 
moisture content of the soil. 

CLASSIFICATION OF THE WATER IN SOILS AND PLANT TISSUES 

The physicist finds it desirable to distinguish between water in the 
solid, liquid and vapor form; the chemist distinguishes between free 
water, water of crystallization and water of constitution. Similarly it is 
convenient for the student of soils and plant physiology to classify water 
according to the form in which it is held in the soil or in plant tissue and 
the consequent uses to which it may be put. No one classification has 
proven most satisfactory for all purposes. Attention is here directed to 
those that seem more useful in explaining the response of the plant to 
varying water content. 

The Response of Water to the Force of Gravity and the Evaporating 
Power of the Air. — The water of the soil is held in three conditions: (1) free, 
or gravitational water, (2) capillary water and (3) hygroscopic water. The 
free or gravitational water is that which moves down through the soil 
under the influence of gravity. It is the surplus water that drains away 
after heavy rains or heavy irrigation, finding its way eventually through 
underground channels to streams or springs or to the so-called ground- 
water level. Capillary water, on the other hand, does not move down- 
ward in response to the force of gravity, but adheres to the soil particles 
in the form of films of varying thicknesses. It does not drain away freely 
with the seepage water, though there is some reduction in its amount 
within a given soil depth if there is a material lowering of the water 
table of the soil. However, it may be lost through evaporation from the 
surface soil. Hygroscopic water is the moisture that is to be found in 
air-dry soil exposed to a moist or saturated atmosphere. Like capillary 
water it exists in the form of thin films adhering to the surface of the soil. 
The films, however, are much thinner than those of capillary moisture 
and the soil retains this hygroscopic water with great tenacity. The 
capillary and hygroscopic moisture together may be regarded as a product 
of what the soil particle can hold against the pull of gravity on the 
one hand and the evaporating power of the air on the other. 

47 



48 



FUNDAMENTALS OF FRUIT PRODUCTION 



The maximum amount of water that a given soil may contain depends on 
the volume of its pore space. Both may range from about 32 to a little over 52 
per cent. 77 This amount of water is equivalent to a 4 to 6 acre-inch precipitation 
and would weigh from 20 to 32 pounds per cubic foot of soil. Naturally these 
large amounts of water are not found in any soil except below the water table line 
or immediately after heavy precipitation or irrigation and before drainage has had 
an opportunity to carry away the surplus moisture. It is the amounts of capil- 
lary and hygroscopic water that a soil will retain rather than its total water-holding 
capacity as determined by pore space that are of interest in fruit growing, for the 
reason that little or none of the free or gravitational water is utilized by the 
plants. For most purposes and under most conditions it is only the capillary 
moisture that they use, though Loughridge 86 is responsible for the statement 
that in some instances plants are able to remain alive, even though they cannot 
grow, in soils whose water supply is reduced to the point where only hygroscopic 
moisture is present. The total amount of capillary water that a soil will retain 
depends not so much on the pore space as on the size of the soil particles 
and the distance from the level of the ground water below. Tables 27 and 28 
show the percentage of water that certain typical soils will hold as capillary 
moisture against the force of gravity. These figures were obtained from soils 
of undisturbed field texture several days after heavy rains so that gravitational 
water had had ample opportunity to drain away. It should be stated in con- 
nection with these tables, that in each case the soil became somewhat more sandy 
at greater depths. 



Table 27. — Amounts of Capillary Moisture Held Against 
Gravity in Certain Typical Soils 77 


the Force of 


Depth 


Sandy loam, 
per cent. 


Clay loam, 
per cent. 


Humus soil, 
per cent. 


First foot 


17.65 
14.59 
10.67 


22.67 
19.78 
18.16 


44.72 


Second foot 


31.24 


Third foot 


21.29 







Table 28. — Maximum Capillary Capacity of Soils for Water 



Percentage 
of water 



Pounds of 
water per 
cubic foot 



Inches of 
water 



Surface foot of clay loam 
Second foot of reddish clay . . 
Third foot of reddish clay . . . 
Fourth foot of clay and sand 
Fifth foot of fine sand 



32.2 
23.8 
24.5 
22.6 
17.5 



23.9 
22.2 
22.7 
22.1 
19.6 



4.59 
4.26 
4.37 
4.25 
3.77 



It is interesting to note that the optimum condition for the growth 
of plants is afforded by a soil when the capillary water amounts to between 
40 and 60 per cent, of the total water-holding capacity of the soil, leaving 



SOIL MOISTURE 49 

from 60 to 40 per cent, air space. Desert plants or plants coming from 
dry climates are more tolerant of deficiency in soil moisture and the opti- 
mum capillary moisture content for these plants is lower. The reverse 
is true of certain other plants that thrive under moist conditions. The 
almond is mentioned by Hilgard and Loughridge 66 as suffering from excess 
moisture when approximately three-fourths of the pore space was filled 
with water. 

The hygroscopic moisture of the soil varies greatly with the composition. 
In sandy soils it may be as low as 2 or 3 per cent, and in coarse sands even lower. 
In ordinary loams it ranges from 4 to 5 per cent, and in heavy clays and adobes 
it may be as high as 8 or 10 per cent. 86 

The Relative Saturation. — Brown 27 suggested that a more useful way 
of expressing the water content of the soil would be in terms of its relative 
saturation. This would take into account the maximum water capacity 
as well as the actual water content and would afford a more accurate 
index of the biological or physiological wetness of the soil than the 
standards of measurement now employed. In commenting upon this 
question of relative saturation he says: 

"The water content alone is . . . but an imperfect index of the soil con- 
ditions. Since soils of different mechanical composition have different capacities 
for water, the same quantity of water produces different changes in humidity in 
these different soils. For example, the quantity of moisture sufficient to saturate 
a given mass of sandy soil is insufficient to saturate a like mass of humous soil. 
The degree of wetness or dryness, of a soil, therefore, really depends on the 
amount of water which the soil can still take in before being saturated. Con- 
sequently, a more perfect index to the 'wetness ' or 'dryness ' of a soil is to be had 
by expressing the water content of the soil in terms of its maximum water capacity, 

,. ,. Water content , . . A , _ , t . _ . . 

the ratio ^ — ; -. r— ■> being termed the Relative Saturation or 

Maximum water capacity & 

the soil . . . This value, and not the actual water content itself, will be the index 

to the ' biological wetness' of the soil ... in comparing two soils whose actual 

moisture contents are different, say, the ratios may indicate that both soils, 

however, have the same degree of wetness, and so, in relation to the physiological 

action of the plant are of similar conditions." 

Resistance to Freezing. — Another classification of the soil water is 
made by Bouyoucos. 17 This classification is based upon freezing point 
determinations with the dilatometer. Water which freezes at or slightly 
below 0°C. is termed free water, that which freezes between 0°C. or a 
little below and — 78°C. is termed capillary or capillary-adsorbed water 
and that which does not freeze except at temperatures below — 78°C. is 
termed combined water. These classes do not coincide exactly with those 
of the classification used before and they serve to bring out some of the 
features of the water supply of the soil that have been overlooked and 



50 FUNDAMENTALS OF FRUIT PRODUCTION 

that investigations indicate are intimately associated with the question 
o£ winter injury. 

Bouyoucos 17 points out that the relative amounts of these forms of water 
vary greatly in different soils. He says: "In some soils only one or two forms 
predominate, while in others all three are about equally represented. In the 
sands and fine sandy loams, it is the free water that predominates, which amounts, 
in some cases, to about 95 per cent, of the total water present; the other 5 per 
cent, consists as a rule, of combined water; capillary adsorbed water is apparently 
not present in these classes of soil. In the loams and silt loams, it is the free 
and combined water which predominates. Here, again the capillary-adsorbed 
water is present in small amounts. In some of the heavy loams all three forms 
are about equally distributed. In clay loams and humus loams and clay, it is 
the combined water which predominates followed by capillary-adsorbed and 
free. Although the amount of free water tends to decrease and the amount of 
the capillary-adsorbed and combined water tends to increase correspondingly as 
the soils ascend from the simple and non-colloidal to the complex and colloidal 
classes. There are many exceptions to this rule." 17 

Of equal importance are the differences in the amounts of free or 
easily frozen water in plant cells, as determined by McCool and Millar, 93 
using the dilatometer. The differences found suggest corresponding 
differences in the amounts of adsorbed water in plant cells. 

The different water-absorbing capacity of plant cells is attributed by Spoehr 129 
to their pentosan content. This is confirmed by the work of Hooker. 69 It seems 
probable, therefore, that the chemical composition of plant tissue, as of soils, 
has a most important bearing on the condition in which its water is held. This 
in turn has a direct relation to the susceptibility of plant tissue to environmental 
changes, a subject that is discussed in greater detail in the section on Tempera- 
ture Relations. 

McCool and Millar 93 measured the amounts of easily frozen water in plants 
grown in soils of high, medium and low water content. They found that the 
plants grown in soils of high water content contained more easily frozen water. 
Rosa 105 has shown that with lower moisture content of the soil there is an increase 
in the pentosan content of the plants grown in it. This amplifies the discovery 
that pentosans are produced under xerophytic conditions and that the water- 
retaining capacity of the cells is thereby increased. 121 The greater amount of 
adsorbed water that such plants contain would mean the presence of smaller 
amounts of free or easily frozen water, such as McCool and Millar found. These 
investigators have also shown a correlation between the depression of the freezing 
point of plant sap and the amount of easily frozen water it contains; the lower 
the freezing point the less easily frozen water is present. 93 This suggests that 
differences in the concentration of cell sap may be due in part to the relative 
amounts of free and adsorbed water. It is obvious that with a given amount of 
soluble material, the concentration of the sap will depend on the amount of free 
water available for its solution. The less the proportion of free water and the 
greater the proportion of adsorbed water the higher the concentration of the 
solution. 



SOIL MOISTURE 51 

These differences in condition of the water present are important in 
practical ways. They explain the increased moisture requirement of a 
plant grown in moist surroundings; their application in cold resistance is 
shown elsewhere ; it is possible that the greater adaptability of some plants 
to varied environments is related to their capacity of forming water 
retaining substances. These water retaining substances represent a 
mechanism for the retention of moisture by living plant cells, a mechanism 
which is entirely distinct from that represented by the anatomical modifi- 
cations characteristic of xerophytic or semi-xerophytic plants. The 
former has to do with the loss of water from the cells to the intercellular 
spaces; the latter with the loss of water from the plant tissue to the 
outside. The two means of protection against water loss may occur 
together in which case the effectiveness of each would be increased, but 
they may be quite independent of each other. 

MOVEMENT OF WATER IN THE SOIL 

After water once reaches the soil, following either natural precipitation 
or irrigation, it becomes subject to the forces of gravity and surface 
tension and in a general way these may be said to control its movement. 
Percolation downward represents the result of the two forces working 
together. Lateral movement and rise by capillarity represent what the 
force of surface tension is able to do in opposition to the force of gravity. 

Percolation. — It has been pointed out that optimum growing condi- 
tions for most crop plants are found when from 40 to 60 per cent, of the 
total pore space of the soil is filled with capillary water. Immediately 
after heavy rains the soil moisture occupies a larger percentage of pore 
space in the soil. Therefore, the movement of water through the soil 
must be considered. In humid regions its vertical movement is of chief 
interest; in irrigated sections both its vertical and its lateral movement 
are important. Few realize the rate at which water percolates through 
the soil and the percentage of the total precipitation or of the total 
amount applied by irrigation that is lost in this way. Table 29 averages 
the percolation data obtained during a period of 34 years at the Rotham- 
sted Experiment Station on a rather heavy loam, or clay loam soil. It 
shows the amounts of water percolating through the soil columns 20, 
40 and 60 inches deep. 

Attention is directed particularly to the great difference between the 
proportions of rainfall removed by seepage in years of light and years of 
heavy fainfall. The figures also show a much higher percentage of 
percolation during winter months when there is comparatively little 
evaporation than during the summer months when the evaporation 
rate is high. As a rule, the lighter the soil, the larger is the percentage of 
percolation water. Consequently in the irrigation of light soils it is 



52 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 29. — Rate of Percolation of Water Through Clay Loam Soil 90 



Inches 

of 
rain- 
fall 



Inches of water drained 
through soil columns 



20 


40 


inches 


inches 


deep 


deep 



60 

inches 

deep 



Per cent, of rainfall per- 
colating through soil 
column 



20 


40 


inches 


inches 


deep 


deep 



60 

inches 
deep 



January . . . 
February. . 

March 

April 

May 

June 

July 

August. . . . 
September 
October. . . 
November 
December . 



2.32 
1.97 
1.85 



89 
11 
36 
73 
67 
52 
20 



2.86 
2.52 



1.82 
1.42 
0.87 
0.50 
0.49 
0.63 
0.69 
0.62 
0.88 
1.85 
2.11 
2.02 



2.05 
1.57 
1.02 
0.57 
0.55 
0.65 
0.70 
0.62 
0.83 
1.84 
2.18 
2.15 



1.96 
1.48 
0.95 
0.53 
0.50 
0.62 
0.65 
0.58 
0.76 
1.68 
2.04 
2.04 



78.5 
72.2 
47.6 
26.5 
23.2 
24.0 
25.3 
23.2 
35.0 
57.8 
76.7 
80.3 



88.4 
80.0 
55.6 
30.0 
26.1 
27.6 
25.6 
23.2 
32.8 
57.5 
76.3 
85.4 



84.5 
75.2 
52.0 
28.0 
23.6 
26.3 
23.8 
21.7 
30.0 
52.3 
72.4 
81.0 



Mean total per year. 



28.98 



13.90 



14.73 



13.79 



48.2 



51.0 



48.0 



Results for: 
Maximum rainfall. 
Minimum rainfall. 



38.70 
20 . 50 



23.50 
7.32 



23.60 
7.90 



24.30 
7.70 



60.7 
35.7 



61.0 
38.5 



63.0 
37.6 



generally necessary to use more water than in heavy soils under similar 
climatic conditions and with the same fruits. The extra amount of 
water required by such soils may be reduced somewhat by lighter and 
more frequent applications, but this too may be carried to an extreme and 
result in an unnecessary waste through evaporation. An illustration of 
this principle is furnished by certain orchards on the Umatilla Irrigation 
Project in eastern Oregon. Many orchards on this project have required 
7 or 8 acre-feet of water in order to bring a crop of fruit to maturity, 
though the trees themselves could use only 9 or 10 inches. Evaporation 
rates in the climate of that section are very high, but the main reason 
for applying 9 to 10 times more than the trees actually use is the extremely 
high percolation through light porous sandy soils and subsoils. 

The Rise Of Water By Capillarity. — It is often thought that much of 
the water that percolates through the soil again rises by capillary action 
and becomes available to the trees later in the season. Investigations 
of recent years tend to minimize the importance of this upward movement 
of soil moisture. The generally accepted opinion of the present may be 
summarized in the following statement by Rotmistrov: 106 "As regards 



SOIL MOISTURE 



53 



the mechanical raising of water, however, by capillary action it may be 
assumed that the limit from which water can make its way upward lies 
much higher than the limit accessible to the roots. All the data at my 
command regarding moisture in the soil of the Odessa Experimental 
field point only to one con- 
clusion, namely, that water 
percolating beyond the depth 
of 40 to 50 centimeters (16 to 
20 inches) does not return to 
the surface except by way of 
the roots." Briggs, Jensen 
and McLane, 23 in reporting 
upon the results of irrigation 
experiments in citrus groves 
in California state that avail- 
able soil moisture below the 
third foot did not prevent 
orange trees from wilting 
when the moisture content 
in the first 3 feet of soil fell 
below its wilting coefficient 
and the roots of the trees were 
limited to the first 3 feet. 
This is a point that must be 
kept in mind in irrigation 
practice for it means that 
trees can utilize the moisture 
supply in the volume of the 
soil that the roots occupy, 
but very little that percolates 
to or stands at a lower level. 
In other words, the tree can 
make use of the water supply 
at 3 or 4 or 5 or 10 feet in 
depth only to the extent that 
it can develop a root system 
that penetrates to these 
depths. 

Lateral Movement of Water in the Soil. — The lateral movement of 
water in soils is likewise dependent largely upon texture, though the 
amount and kinds of soluble mineral salts, the soil colloids, the organic 
material and other factors have their influences. In open, porous soils, 
water spreads laterally to a considerable distance and with comparative 
rapidity. In heavy, compact soils, its lateral spread is slight and slow. 





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Fig. 3. — Rate of movement of moisture in soil 
in horizontal open flumes. Figures in circles indi- 
cate points at which that number of liters of water 
had been taken up. The dotted line for flume No. 
71 (covered) is for comparison with flume No. 70 
(open). (After McLaughlin. 96 ) 



54 FUNDAMENTALS OF FRUIT PRODUCTION 

For instance, in one experiment on a heavy soil in California, after an 
irrigation considered sufficient to last about four weeks, the moisture 
was found to have penetrated laterally only about eighteen inches from 
the irrigation furrow. 23 Figure 3 shows graphically the rate of this 
lateral spread as it takes place through the force of capillarity and unaided 
by gravity. The spacing of irrigation furrows must be made accordingly, 
if the entire volume of the soil is to be wetted. It is for this reason that 
basin irrigation or flooding is sometimes preferred to furrow irrigation in 
comparatively heavy land. 

THE DISTRIBUTION OF FRUIT TREE ROOTS AS INFLUENCED BY SOIL 

MOISTURE 

The size and distribution of the root system depends upon the opera- 
tion of many factors, such as the moisture supply, aeration of the soil 
and nutrient supply. In most cases it is impossible to assign to each 
factor the part it has played, but as they are more or less interdependent 
they may be discussed together. 

The Ideal Root System. — Deep rooting is desirable for the purpose 
of making the water (and nutrient) supply contained in a large volume 
of soil available to the plant. For the same reason there should be at 
least a moderate lateral spread. In other words the tree, or other 
fruit-producing plant, that is equipped with an extensive root system 
will be able better to endure extremes of drought or temperature or 
exceptional demands for a supply of nutrients, than one with a limited 
root system. Plants grown in a comparatively concentrated nutrient 
solution or in rich soil have roots that are shorter, more branched and 
more compact than those grown in a weak nutrient solution or in a 
poor soil. Changing fertility is one explanation of the marked contrasts 
in the degree of ramification of roots as they penetrate different strata. 19 
The ideal root system is, therefore, not the one with branches that reach 
out or down the farthest, but the one that more or less fully explores 
and occupies the soil to a reasonable depth and within a reasonable 
radius. Otherwise, it would be necessary to regard the root system pro- 
duced only in an infertile soil as the ideal. 

Specific and Varietal Differences in Root Distribution. — Depth of 
rooting and lateral spread of roots depend in the first place on the species 
or variety of plant. Some, like the walnut and pecan, are character- 
istically deep rooted ; others like the spruces and hemlocks and the river 
bank grape (Vitis riparia) are characteristically shallow rooted. The 
roots of certain fruit varieties, like the Wealthy apple, are strong, stocky 
and far ranging; those of other varieties, like certain strains of the Doucin, 
are short, slender, compact and much branched. These characteristics 
should be borne in mind when selecting fruits or fruit stocks for particular 



SOIL MOISTURE 55 

soils and when considering the influence of various environmental factors 
and cultural practices upon root distribution, for though root distri- 
bution is influenced profoundly there are limits to the plasticity of any 
species; nothing stated in this connection should be construed as im- 
plying that these usual limits for the species or variety may be exceeded. 

The Distribution of Tree Roots under Varying Conditions. — Tree 
roots often range deep, but such investigations as have been reported 
show a surprisingly shallow root system in most of our orchard planta- 
tions, at least in the humid regions. 

In the Hood River Valley, Oregon and in Ohio. — For instance a report 
upon the condition of the root system of apple trees in the Hood River 
valley states: 

"It was found that the majority of the feeding roots of fruit trees of bearing 
age were located from 3 to 10 inches below the surface of the soil." 2 A discussion 
of the root systems of apple trees in Ohio includes the following statement: "The 
main root systems, of apple trees, under the different methods of culture (clean 
culture with cover crops, sod culture, and sod mulch), were found to be at a sur- 
prisingly uniform depth — the greater portion of the roots, both large and minute, 
being removed with the upper 6 inches of soil. . . . The fibrous or feeding-root 
system of a tree under annual plowing and clean culture with cover crops, practi- 
cally renews itself annually — pushing up thousands of succulent, fibrous rootlets 
to the very surface of the soil where they actually meet with the steel hoes or 
spikes of the cultivator or harrow, especially in seasons when moisture is abun- 
dant. Apparently but a small percentage of these rootlets penetrate the lower, 
more compact colder soil, but they come to feed where warmth and air and mois- 
ture combine to provide the necessary conditions for root pasturage. As a matter 
of fact, these feeding rootlets are cleanly pruned away by the plowshare each 
succeeding year, and without apparent injury to the trees or crops." 54 

The writers then go on to state that the destruction ol the roots in 
the upper 2 or 3 inches of soil by summer drought or by winter cold re- 
sults in no serious injury to the tree, as those ranging deeper, 4 to 6 
inches, can take care of the tree's requirements. 

In a Gravelly Loam, Underlaid by Hardpan, in Maine. — Some valuable 
data on the root distribution of apple trees growing under different soil 
conditions were obtained by Jones 73 in Maine. Figures 4 and 5 show photo- 
graphs of the tree roots obtained from a square foot of soil midway be- 
tween two Baldwin trees set 27 feet apart and about 28 years old. The 
photographs show the roots in successive layers of soil 4 inches thick. 
This soil was a gravelly loam to a depth of 2 or 2^ feet where a rather 
impervious hardpan was encountered. Figure 4 shows roots growing in 
a rather wet portion of the orchard; those in Fig. 5 were from a drier 
portion. The tops of these trees were not meeting, yet in both the wet 
and dry areas their roots were interlacing and the soil to a depth of over 
2 feet was more or less thoroughly exploited. Though the greatest ex- 



56 



FUNDAMENTALS OF FRUIT PRODUCTION 




tf 9 



rz 


rt 





id 










t> 


o 


■j 





c 








at 




u 




T3 




>, 





P4 



SOIL MOISTURE 



57 




58 



FUNDAMENTALS OF FRUIT PRODUCTION 



pansion of the root system was in the 4- to 8-inch layer, there was a 
fairly large number of roots 20 inches deeper. There was also much 
better expansion of the root system at both upper and lower levels in 
the drier soil than in the one classed by Jones as a little too wet for the 
best growth of the apple tree. The question is raised by Jones as to 
whether interlacing of roots is not evidence that for a number of years 
these trees had been suffering from lack of room, a suggestion supported 
by the indifferent performance of the orchard for some time previous. 

Table 30 shows the length of the roots, in feet, found in each cubic 
foot of soil at successive distances from the tree trunk. These measure- 
ments were taken for a Milding apple tree 9.33 inches in diameter 2 feet 
from the ground, with an 11-foot spread of branches, and growing in a 
stony loam. The last column shows the computed length of roots for the 
cylinder of soil 1 foot in thickness surrounding the tree at a given distance 
from the trunk, assuming that the section examined is typical for the 
entire area of which the tree is the center. Figure 6 shows graphically 
the data presented in Table 30. They afford some idea of the relatively 
extensive development of a tree's root system under conditions that are 



Table 30. — Root Distribution of a 25-year Old Apple Tree, Measured by 

Sections 
(After Jones 73 ) 



Distance of 

section in feet 

from tree trunk 


Length of roots 

in first 6- 

inch layer of 

soil, feet 


Length of roots 

in second 6- 

inch layer of 

soil, feet 


Total length 
of root in 

cubic foot of 
soil, feet 


Computed 

length for 

cylinder about 

trunk, feet 


1 


112 


32 


144 


144 


2 


66 


109 


175 


16.50 


3 


19 


74 


93 


1460 


4 


3 


72 


75 


1650 


5 





28 


28 


792 


6 


3 


48 


51 


1712 


7 





48 


48 


2008 


8 





32 


32 


1508 


9 


4 


72 


76 


4059 


10 





35 


35 


2089 


11 


5 


37 


42 


2771 


12 


4 


16 


20 


1445 


13 


3 


26 


29 


2278 


14 





18 


18 


1527 


15 





12 


12 


1093 


16 





8 


8 


779 


17 


6 


2 


8 


829 


18 





8 


8 


880 


19 





7 


7 


814 • 


20 





H 


H 


61 



SOIL MOISTURE 



59 



presumably more or less common. In this case plowing and cultivating 
to a depth of 6 inches would have destroyed a little less than one-tenth 
of the conducting roots. The percentage of the very small absorbing 
and feeding roots would not necessarily be the same. Over 19,000 of 
the total of 29,547 feet of conducting roots, in other words about 65 per 
cent., lie beyond the spread of its branches. Probably the proportion 
of feeding roots is still greater. Irrigation water and fertilizers should be 
distributed accordingly; the treatment of the small area of soil immediately 
surrounding a large bearing tree which is difficult of access with the tools 
of cultivation would seem to be of small importance so far as either water 
or nutrient supply is concerned. 



120 

no 

100 
; 90 



o^lO 
°j 60 



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/ 






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234-56789 10 



12 13 14 15 16 II 18 19 20 



Distance from Tree, feet 



Fig. 6. — Distribution of apple roots in surface six inches and second six inches in a 
soil section one foot wide in rather heavy loam. Solid line shows surface layer; broken 
line shows second layer. (After Jones. 13 ) 



In a Thin Gravelly Loam, Underlaid by Rock, in Maine. — The data 
given in Table 31 represent extreme conditions. They are for an under- 
sized, stunted seedling apple tree probably 40 years old, on level ground 
at the top of a hill thinly covered with a rocky, gravelly clay loam The 
soil was less than a foot deep and was underlaid by rock or ledge or with a 
heavy clay mixed with gravel. For many years the orchard had been in 
pasture and the trees, having received practically no care, had experienced 
a hard struggle for existence and many had died. 

Without doubt, limited nutrient as well as limited moisture supply had 
been an important factor in forcing this tree to extend its root system so 
far and wide in order to hold on in its struggle for existence. Whatever 
may have been the exact combination of factors leading to this develop- 
ment it shows a marked power of adaptation on the part of the plant. It 
also carries the suggestion that in soils where deep rooting is impossible 
the spacing of trees and other fruit plants should be much wider than 
under more favorable conditions. 



60 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 31. — Root Distribution of a 40-yeak Old Apple Tree in a Thin Rocky 

Soil Under Sod for Many Years 

(After Jones 73 ) 



Distance 


Length 


Length 




Distance 


Length 


Length 




of section 


of roots 


of roots 


Total 


of section 


of roots 


of roots 


Total 


from 


in top 


in next 


length, 


from 


in top 


in next 


length, 


trunk, 


6 inches, 


6 inches, 


feet 


trunk, 


6 inches, 


6 inches, 


feet 


feet 


feet 


feet 




feet 


feet 


feet 




1 


64 


96 


160 


16 


32 


2 


34 


2 


98 


22 


120 


17 


10 





10 


3 


20 


50 


70 


18 


6 


7 


13 


4 


34 


80 


104 


19 


6 


14 


20 


5 


54 


34 


88 


20 


8 


12 


20 


6 


22 


4 


26 


21 


8 





8 


7 


14 


7 


21 


22 


11 


3 


14 


8 


17 


18 


35 


23 


3 


8 


11 


9 


16 


26 


42 


24 


3 


5 


8 


10 











25 





7 


7 


11 





10 


10 


26 


2 





2 


12 


6 


9 


15 


27 


5 


7 


12 


13 


12 


12 


24 


28 





2 


2 


14 


28 


23 


51 


29 





2 


2 


15 





18 


18 




' 







In Dwarfs. — In contrast with the comparatively extensive root 
systems of trees growing in the field are those of dwarfs occasionally 
grown in the garden or under glass whose growth is restricted by various 
means. Sometimes resort is made to root pruning; sometimes the roots 
are restricted by planting in pots or tubs. Such trees develop very com- 
pact and much branched root systems that exploit very completely the 
soil within their range. Dwarf trees with such restricted root systems 
are much more subject to injury from extremes of moisture than standards 
with unrestricted root systems. Consequently their successful culture 
necessitates much greater care in watering, fertilization, pruning, exposure 
to light and management in general. 

The Influence of Soil Moisture Content. — Within the ranges possible 
for the different species, depth of rooting depends to a very important 
extent on soil moisture and the correlated factor, aeration. Roots do 
not grow and branch freely in a very dry soil, or in one that is approach- 
ing a water-logged condition. The water-logged soil probably inhibits 
root growth and activity through a lack of aeration; the dry soil through 
a lack of the stimulating effect of the water itself. Figure 7 gives some 
idea of the influence exerted by the percentage of soil moisture on root 
formation and root distribution when other factors are as uniform as it is 
possible to make them. In this case, however, the soil moisture did not 



SOIL MOISTURE 



61 



bandy 
Clay 



Pure 
Sand 



approach sufficiently near the saturation point to check root formation. 
When roots find an abundance of water close to the surface they branch 
freely through the surface soil and show little tendency to go deeper, 
particularly if conditions are more and more unfavorable for root develop- 
ment at greater depths. These two 
factors together probably explain the 
comparatively shallow rooting of 
most tree, bush and vine fruits in a 
large portion of the humid region. 
Compact, water-logged subsoils or 
a high water table prevent the roots 
from penetrating deeply. The sur- 
face inch or so is too dry during a 
major portion of the growing season 
to encourage root growth ; the result is 
a distribution of most of the roots be- 
tween the depths of 3 to 10 or 15 
inches. 

When, however, moisture and 
aeration conditions are favorable for 
root development at considerable 
depths, deep penetration occurs. 
Thus Hilgard and Loughridge 66 state 
that on some of the silty "low mesa" 
soils of California the roots of cherry 
and prune trees are frequently found 
at depths of 20 to 25 feet. Such deep 
rooting is also characteristic of fruit 
trees in the loose soils along the 
Mississippi and Missouri rivers. 
These are soils, however, with no 
hardpan or plowsole and with the 
water table many feet below the sur- 
face. In them soil grades insensibly 
into subsoil. Indeed, subsoil in the 
sense in which the term is generally 
used, does not exist except below the 
region of this exceptional root pene- 
tration. It hardly need be pointed out that trees in such soils seldom 
suffer from drought, even though there may be a series of dry years. 

When plants, accustomed to growing in a soil where shallow rooting is 
necessary, are transplanted to one in which deep penetration is possible, 
they first send out shallow lateral roots, their distribution being much 
like that of the same plant in the region or soil from which it came. They 




Fig. 7. — Influence of soil moisture 
upon root distribution of Kuhnia gluti- 
nosa. {After Weaver. 131 ) 



62 FUNDAMENTALS OF FRUIT PRODUCTION 

probably encounter in the surface layers, shortly after the time of setting, 
those conditions of air and moisture approaching the optimum for growth. 
Then as the season progresses and the surface soil dries, the roots in 
many cases turn down and send branches into deeper layers and a distri- 
bution is effected resembling that of native plants. 63 This may be looked 
upon as a kind of adaptation, an accomodative change, to meet new con- 
ditions of environment. That this change in rooting habit is very largely 
a response to moisture and aeration conditions is indicated by the fact 
that with a rise in the ground water table from heavy irrigation the roots 
are again forced to occupy only a shallow layer of soil. This condition is 
found in some of the orange groves of California. 63 Three or four feet 
beneath the surface the soil is so water-logged that roots will not penetrate 
and the top 6 or 8 inches are so filled with feeding rootlets that each 
cultivation results in more or less serious root pruning. Trees under such 
conditions require heavier irrigation and more fertilization than those 
with deeper roots and, what is perhaps more important, they are more 
sensitive to extremes of any kind affecting the roots either directly or 
indirectly. Consequently they are more exacting in their cultural 
demands. The same danger from heavy irrigation is met in deciduous 
fruit production. Thus it has been found in Utah that raising the water 
table even temporarily by irrigation causes the death of the deeper roots 
and results in a kind of root pruning or root training and that the general 
shape of the root system of the tree may be controlled more or less by the 
distribution of the irrigation water. 8 One of the most difficult problems 
in many irrigated sections is to apply the water in such a way that plants 
are not made surface feeders and the natural advantages of a deep soil 
lost. 

The Influence of Cultivation.- — Allen 2 found that tillage methods influenced 
root distribution in the Hood River district. He reports that where clean 
culture had been practiced without the use of the plow but with disk and other 
cultivators "a thick mat of fibrous roots was found immediately below the soil 
mulch. ... In the few restricted areas that received neither cultivation nor 
irrigation, the roots were found to be distributed from near the surface to 1 
foot and 16 inches in depth. Under sod and irrigation conditions the roots were 
quite uniformly distributed from near the surface to 2% feet in depth." Immedi- 
ately under the loose surface soil of the cultivated areas he found an impervious 
hardpan or plowsole had developed, which was dry at the time of this examina- 
tion. The untilled and irrigated land did not have this hardpan layer. 

Different tillage methods had resulted in great variation in the physical 
character and moisture content of the soil between the depths of 6 and 
30 inches, and in corresponding variations in root distribution. Evidently 
the varying tillage methods used in certain Ohio orchards 54 did not 
change materially the character of the soil below a depth of 6 or 10 
inches and since few roots developed in it below this depth, root distri- 



SOIL MOISTURE 



63 



bution was influenced but little in this particular case. Cultivation is 
mentioned often as a means of forcing deeper rooting of fruit trees and 
sod culture as encouraging shallower rooting. These practices often 
have these effects, but they may have no such effect, as in the Ohio investi- 
gation cited, or they may have the opposite effects, as in Hood River. 
This brings out the point that tillage methods as such are not to be 
regarded as direct means of influencing root distribution, but as means 
of altering the physical and chemical condition of the soil and thus indi- 
rectly leading to shallow or deep penetration. Root growth and distri- 
bution is a response to these physical and chemical conditions. It is 
noteworthy that in the Hood River orchards many of the symptoms of 
drought injury were associated with extreme shallow rooting — premature 
dropping of the foliage, dieback and fruit-pit. 

Interesting data concerning the effect of cultivation on root distri- 
bution are afforded by the figures in Table 32. Cultivation along one 
or both sides of the tree row reduced the absolute lateral spread and the 
ratio between the lateral spread and height of the trees. The greater 
reduction accompanied cultivation along both sides. In the cultivated 
soil the tree roots did not have to range so wide to meet the actually 
increased water requirements of the trees as in the uncultivated land. 
Incidentally the figures in Table 32 throw some light on the lateral 
spread of tree roots as compared with the spread of their branches. 
Though spread of top is not given it is reasonable to assume that in this 
species it is less than tree height. It is often said that the lateral spread 
of the roots is about equal to the lateral spread of the branches. In 
uncultivated ground it was in this instance more than twice as great. 

Table 32. — Effect of Cultivation Upon Root Spread of the Osage Orange 13 



Amount of 
cultivation 


Cases 
measured 


Average height 
of trees 


Average root 
extent 


Average root extent; 
proportion to height 


None 


8 
25 
35 


20.0 
17.2 
21.7 


43.7 
28.9 
29.2 


218 7 


One side of trees . . 
Both sides 


167.8 
134.5 



Mason 91 cites an instance in which the olive grown in an extremely dry soil 
and climate had a root system radiating 10 to 11 feet in nearly all directions when 
the top was only 6 feet in height, had a spread of only 7 feet and a trunk diameter 
of 3% inches. In this case there was a total of 185 feet of roots % inch or 
more in diameter and the area occupied by roots of this size was about nine 
times that of the spread of the branches. This fruit as it grows in the Sfax 
region of Northern Africa furnishes a good illustration of the adaptation of the 
root system to moisture conditions. There it sends out numerous roots which 
run for long distances comparatively close to the surface where they can make 
use of the moisture that penetrates only a few inches into the ground at the 
time of the infrequent light rains. 



64 FUNDAMENTALS OF FRUIT PRODUCTION 

The Influence of Soil "Alkali." — It should not be inferred from the 
emphasis that has been placed upon moisture and aeration in determining 
root distribution that other factors are of little significance. Other 
factors are often controlling. 

For instance in reporting upon an investigation of the effects of alkali on 
citrus trees Kelley and Thomas 76 state: "It is especially interesting that the 
roots of the lemon trees have not penetrated deeply in this soil, more than 95 
per cent, of them being within 18 inches of the surface. There is probably 
some connection between this fact and the higher concentration of alkali salts 
found in the third and fourth feet." 

Applications to Orchard Practice. — The whole subject of the distribu- 
tion of the root system of orchard plants may be summarized in this way: 
though different species of plants and different varieties of the same 
species have characteristic habits of root growth, the extent and the 
distribution of their root systems are profoundly influenced by environ- 
ment. Root development, both as to amount and direction, may be 
regarded as a response of the plant to this environment. The functioning 
of that part of the plant above ground is conditioned to a very important 
degree by the functioning of the part of the plant below ground, and 
therefore by the distribution of the roots in the soil. Root distribution 
is under control to the extent that soil conditions — texture, moisture, 
aeration and nutrient supply — are under control and to a certain extent 
by the pruning that is afforded the top, a matter discussed in detail later. 
If the soil is one in which these conditions are not favorable for a suitable 
root distribution or in which they cannot be made favorable, it should 
not be devoted to fruit culture, because fruit culture cannot be successful 
on it. As soon as the orchard is planted, or before if possible, and as 
long as the orchard remains, it is well to study from year to year the way 
in which various soil treatments influence those factors determining root 
distribution and then employ those practices that lead indirectly toward 
ideal root systems. Orchards do not die out or become unprofitable only 
because of fungi, bacteria, summer drought or winter cold. These are 
always possible contributing factors and often determining factors, but 
in many cases the fundamental cause of distress is a root system inade- 
quate for requirements of the tree in an emergency — inadequate perhaps 
because too shallow, or in too severe competition with the roots of other 
plants or because it is not exploiting enough soil. Sometimes, though 
the contributing causes to the death or failure of the trees may be un- 
avoidable, the fundamental factor may be completely under control. 

Summary. — In terms of response . to gravity and the evaporating 
power of the air, soil moisture may be classified as gravitational or free, 
capillary and hygroscopic. Only the capillary moisture is available to the 
plant in any considerable amount. The capillary supply is derived from 



SOIL MOISTURE 65 

precipitation and irrigation or to a limited extent from the gravitational 
water that reaches the ground water level. The optimum water content 
for the growth of plants is reached when its relative saturation is approxi- 
mately 50 per cent. A certain percentage of the soil moisture is held in a 
capillary adsorbed or colloidal form and is not frozen at the ordinary 
freezing point of water. This portion of the water supply is of great 
importance to the plant. The evidence indicates that a part of the water 
of plant tissues is held in a similar manner and that this moisture is 
significant in determining drought and frost resistant qualities of the 
tissue in question. The percentage of the rainfall that percolates 
beyond the range of the tree roots varies greatly with many factors, total 
precipitation being one of the most important. Comparatively little 
water that percolates beyond the range of the roots becomes available 
for later use through capillary rise. The lateral movement of soil 
moisture depends principally upon soil texture and the method by which 
irrigation water is applied to the soil should be determined accordingly. 
Root distribution is governed first of all by the growth characteristic 
of the species or variety in question. To an important extent, however, 
it is influenced by soil conditions, particularly soil moisture and soil 
aeration. A deep, moderately wide-ranging root system is preferable to 
one that is shallow, wide spreading or narrow. Though the great major- 
ity of the roots of most orchard trees are in the upper foot or fifteen inches 
of soil, there is little evidence that ordinary tillage results in an injurious 
root pruning. Shallow soils, soils underlaid by hardpan or with a high 
water table, should be avoided for fruit culture because of the restricted 
root range that they necessitate and the consequent susceptibility to 
drought injury of one kind or another. Depth of rooting can be con- 
trolled to a considerable extent by cultural practices, such as tillage, the 
use of cover crops or intercrops of different kinds, irrigation and drainage. 



CHAPTER V 

THE RESPONSE OF FRUIT PLANTS TO VARYING CONDITIONS 
OF SOIL MOISTURE AND HUMIDITY 

Water as a factor in growth thus far has been discussed only in its 
general importance in the development of the plant as a whole. There 
are, in addition, certain specific responses made by the plant to a varying 
water supply. 

Influence of Soil Moisture on Vegetative Growth. — One of the most 
important of these specific responses is in new tissue formation, an in- 
crease in size or bulk. Data have been presented in Table 19 showing 
the influence that various methods of culture, such as tillage, tillage and 
cover crops and artificial mulches, have upon vegetative growth measured 
by trunk circumference. 

New Shoots and Their Leaves. — Table 33 gives certain averages found 
by Hedrick in sod-mulched and cultivated plots in a New York apple 
orchard. Every phase of vegetative growth measured showed a gain 
from tillage. Moreover the tillage plot averaged considerably higher 
in moisture during the growing season. Probably much of the influence 
of tillage was due to the increased moisture available in the soil, yet it is 
difficult to say how much is to be attributed to this factor and how much 
to the influence of the tillage on plant nutrients, particularlv nitrates. 



Table 33. — Influence of Tillage Methods Upon Vegetative 

Apples 59 


Growth in 




Sod 


Cultivated 


Average length of new laterals in inches 

Average number of new laterals per year 


3.40 
1.90 
0.87 
1.10 


6.70 
4.40 


Average weight of leaves in grams 

Average gain in trunk diameter in inches in 4 years 


1.15 
2.10 



More direct evidence of the effect of water on vegetative growth is 
furnished by certain orchard irrigation experiments. The following 
quotations from a report on an investigation in Utah bear on this point. 
"Frequent applications of irrigation water applied to peaches on a 
gravel loam (about 15 feet deep) at intervals of 7 or 8 days produced a 
more continuous and greater total twig growth than the same total 
amount of water applied with larger applications at intervals of every 
10 to 12 days. The more porous the soil the more frequently the trees 

66 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 



67 



should be watered. . . . With varying times of application of irrigation 
water the season of most rapid twig growth is during the season of 
watering." 11 Barss, 9 reporting upon the results of some pot irrigation 
experiments with pears, states: "The most noticeable variation in 
response to the application of different amounts of water, was found in the 
development of the new wood. All the lots started vegetative growth at 
about the same time . . . but terminal bud formation took place early 
on the poorly watered trees and much later on the trees of the other lots. 
Furthermore there were great differences in the rate of wood growth in 
these different lots while they were actually growing. . . . The spurs 
on the better-watered trees were larger and more vigorous. . . . From 
leaf samples, collected and weighed in order to bring out any existing 
differences in weight, it is apparent that, on the average, the leaves 
in the lots receiving most water were far heavier than those in the lots 
receiving less water." He also found the leaves on the trees receiving the 
smallest water supply were variable in both size and shape, their petioles 
were slender, their lower surfaces were markedly pubescent and their 
color was dark green. Callus tissue formed much more frequently on the 
well watered trees. 

Annual Rings and Trunk Circumference. — The results of study on the 
relation between tree growth and total yearly rainfall in Arizona are 

30 



120 



£ n 



x-*-x 


X 

* 
It* 

iy\ 






A 7 k 




V »■ * / \ 


J ^ X 


\t* x/' *A 
V* //x »\ 

\Kyt 1 V 


j x \ii 




x y wi 


• \^ 5? 





1870 



1880 



1890 



1900 



1910 



Fig. 8.— Actual rainfall compared with rainfall calculated from growth of trees, 
Arizona. Solid line equals calculated rainfall. Broken line equals observed rainfall. 
(After Douglass. 72 ) 

interesting in this connection. Under the comparatively arid conditions 
of that region the correlation between the two was found to be so close 
that with a knowledge of the total rainfall of any one year the average 
increase in diameter of trees could be estimated with an average accuracy 
of 82 per cent.; conversely, knowing the average diameter increment 
of a small group of forest trees for any one year it was possible to estimate 
with equal accuracy the total precipitation of that year. Figure 8 shows 
graphically the closeness of this correlation. Huntington 72 employed 
this method of estimating annual rainfall for the study of climatic varia- 
tions during the last 1 ,000 years, obtaining growth records from the giant 
Sequoias of California. Hartig, 57 however, found that in parts of 
Germany where low moisture content of the soil apparently is not the 
limiting factor to growth, the beech makes a smaller annual ring during 



68 



FUNDAMENTALS OF FRUIT PRODUCTION 



seasons that are cold and wet than during years of more nearly average 
temperature and humidity. The decreased growth during the wet 
season may be correlated with poorer aeration in the soil. 

Moisture Supply and the Growth Period in Early Spring. — Most 
deciduous fruits have a short period of very rapid vegetative growth in the 
spring, followed by a longer period of comparatively slow growth that 
precedes the resting stage. That this is a characteristic of most deciduous 
woody plants is brought out by data condensed in Table 34. Of the 
70 species of trees, shrubs and vines considered hardy enough for outdoor 
culture in central Michigan approximately one-fourth had completed 
their shoot growth and formed their terminal buds by June 1, and over 
two-thirds had reached a similar stage by June 20. In no case was there 
appreciable shoot growth before May 1. Gourley 53 states that this 

Table 34. — Numbers of Trees, Shrubs and Vines Completing Shoot Growth 

at Different Dates 
(After Bailey 7 ) 





Date of terminal bud formation 




June 1 or 
earlier 


June 1 to 
10 


June 10 to 
20 


June 20 to 
July 1 


July 1 to 
15 


After July 
15 


Number 


16 
23 


8 
11 


24 
34 


14 
20 


5 

7 


3 


Per cent 


4 











period of rapid growth in the apple lasts only about 25 days in New 
Hampshire and that it is during this period that external factors, such 
as moisture, have their greatest influence upon new tissue formation. 
In his work approximately 43,000 measurements were taken and his 
data point to the conclusion that there was no very close correlation 
between the humidity and rainfall curves and the growth curve during 
this period, though it was not possible to control all factors under field 
conditions. The growth curve showed a closer correlation with tem- 
perature than with any other factors studied. In Idaho, irrigation of 
apple trees after July 15 had no effect upon shoot growth but as a rule 
the more irrigation water applied before July 1, the greater was the shoot 
growth. 124 A similar correlation between growth and soil moisture 
during the months of May, June and July has been observed in Indiana 138 
and it was in the plots with the lowest water content that there was the 
closest correlation between growth and soil moisture. With moisture 
conditions approaching the optimum, an increased rainfall or surplus irri- 
gation water has comparatively little influence in forcing growth. 

Pearson 102 has made a valuable contribution to the knowledge of 
the importance of an adequate soil moisture supply during the com- 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 



69 



paratively short period of rapid vegetative growth. Figure 9 presents 
graphically the results of his series of observations upon yellow pine 
seedlings near Flagstaff, Arizona. 

In commenting upon the data presented in this figure he says: "Contrary 
to what might be expected, there is no apparent relation between height growth 
and annual precipitation, summer precipitation or winter precipitation, in fact, 
the growth from year to year often varies inversely with the precipitation for 
any of these periods. When it is considered that of the total annual precipi- 
tation at Fort Valley, the mean amounting to about 23 inches, approximately 40 
per cent, comes during the winter months (December to March), 30 per cent, 
during July and August, and less than 10 per cent, during the spring months 
(April and May), the foregoing statements are startling. In order to clarify the 
problem, it is necessary to analyze the growth habits of Western yellow pine as 
well as the climatic and soil conditions under which it grows in this locality. 




1909 1910 1911 1912 



1915 



1916 1917 



1913 1914 
Year 

Fig. 9. — Seasonal precipitation and annual height growth of western yellow pine 
saplings from 1909 to 1917. a, Annual precipitation; b, Winter precipitation (December- 
March preceding the corresponding year's growth) ; c, Summer (July-August) precipita- 
tion; d, Annual height growth; e, Spring (April-May) precipitation. (After Pearson. 102 ) 



The terminal shoots begin to elongate about the middle of May, and by July 1 
they have practically completed their growth. Thus it appears that the entire 
height growth occurs during the period of lowest precipitation of the year. From 
the middle of May to the middle of July the rainfall is normally less than one half 
inch, and comes in such small showers as to be of no benefit to deep-rooted plants. 
It is evident, therefore, that the moisture utilized in making this growth is drawn 
almost entirely from a stored supply. It is also evident that the midsummer 
rainfall, since it does not begin until July, when height growth has practically 
ceased, is of little or no consequence, as far as the current year's height growth is 
concerned. The water storage which makes growth possible is mainly the 
result of the preceding winter's precipitation; but it is the supplementary sup- 
ply in April and May which determines whether the growth is to be above or 



70 FUNDAMENTALS OF FRUIT PRODUCTION 

below normal. ... It is evident from the precipitation figures for 1913 that 
the pines in that year depended entirely upon winter precipitation for their height 
growth. Since the total precipitation in April, May, and June was only 0.25 
inch, it may be readily seen that an addition of 2 or 3 inches during this period 
would have resulted in an appreciable increase in soil moisture and presumably 
in height growth. Such was the case in 1914 and in a more marked degree in 1915 
and 1917. If, as is often the case, the first of April marks the end of the season's 
storms, a dry period of 3 months prior to the beginning of the summer rains may 
be expected. Since yellow pine, on account of the low temperature, does not 
begin growth until about the middle of May, a dry period of 6 weeks intervenes 
between the last storm or the disappearance of snow and the beginning of growth. 
During this period a large portion of the stored moisture supply is dissipated 
without benefit to the tree. If, on the other hand, belated storms continue 
through April and into May, the stored water supply is not only conserved, but 
may be actually augmented. A typical example of the first type of spring was in 
1916. Despite a winter precipitation of over 16 inches, the highest on record in 
9 years, soil moisture conditions, after it became warm enough for growth, were 
decidedly below normal. . . . The years 1915 and 1917 are examples of the 
second type of spring. The winter precipitation was only 9.4 inches in 1914-15 
and 6.1 inches in 1916-17, but in both years the precipitation between April 
1 and May 15 was around 6 inches." 

The "Second Growth" of Midsummer or Late Summer. — A second 
period of rapid vegetative growth frequently occurs in late summer or 
fall. Usually it takes place after terminal bud formation on both spurs 
and shoots in the case of spur bearing species. Sometimes the terminal 
buds on the shoots "break" and a new shoot growth is pushed out; 
sometimes terminal buds on many of the spurs "break" and a secondary 
spur growth takes place and sometimes the lateral buds, rather than 
the terminals, initiate this new shoot growth. In some instances terminal 
bud formation has not yet occurred in the primary shoots of the season, 
though growth has slowed down very materially, so there is a sudden 
flush of rapid vegetative development. Occasionally this "second 
growth," as it is generally called, is as extensive in amount as that made 
early in the season, though this is not usually the case. Without doubt 
nutritive conditions within the plant and in the soil have something to 
do in determining "second growth" but the fact that it occurs almost 
invariably after heavy rains or irrigation following a drought, leads to 
the conclusion that it is due at least in part to changed moisture con- 
ditions. It is to be regarded as a phenomenon likely to accompany irregu- 
larity in moisture supply late in the season, and is a response of the 
plant to disturbed moisture relations. This second growth is sometimes 
accompanied by fall blooming in some of the tree fruits. Without 
doubt the "flush" of certain evergreen plants of tropical countries is 
a related phenomenon. It sometimes gives rise to two "annual" rings 
in one season in the trunks and limbs of trees and other woody plants. 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 71 

If this second growth comes fairly early so that the new tissues have 
time to harden and mature properly before winter freezing, little harm 
may result, but often when it comes late in the season the tissues do not 
mature thoroughly and serious winter killing or winter injury follows. 
It is doubtful if, irrespective of susceptibility to winter injury, much 
"second growth" is desirable in sections with more or less severe winter 
weather, for there is reason to believe that the tissues are formed at the 
expense of stored materials that could be used perhaps to better 
advantage the following spring and summer. 

Influence of Water Supply on the Development of Fruit. — The 
influence of soil moisture on the development of the fruit is no less 
important than its influence on vegetative growth. 

Size. — The largest fruits are found on the best watered trees and 
there is abundant experimental data to show the effect of soil moisture 
upon fruit size. Thus Hedrick, 59 who found his tillage plots to contain 
more soil moisture than his sod-mulch plots reports the average weight 
of apples from the cultivated trees to be 7.04 ounces while the average 
weight of those growing in sod was only 5.01 ounces. This difference 
of 40 per cent, was presumably due mainly to the difference in moisture 
supply and accounts in large part for the difference in yield between 
the two plots, which averaged 36 barrels per acre. 

In the discussion of the influence of soil moisture upon vegetative 
growth it is pointed out that new shoot growth and new leaves are made 
early in the season and it may be only during a comparatively short 
period in spring and early summer that this growth is influenced in amount 
by soil moisture. On the other hand, most of the growth of the fruit 
tissues takes place after midseason and therefore it is reasonable 
to believe that soil moisture exerts its greatest influence on their 
development during the last half of the summer and during the autumn. 
That this is actually the case is indicated clearly by a number of irriga- 
tion experiments. In Idaho, irrigation of winter apples before July 10 
had very little influence on their size, though irrigation after that date 
had a very decided influence. 124 Batchelor 11 , in reporting upon the 
results of irrigation experiments with peaches, states: "No amount of 
water applied early in the season to a crop of peaches on a gravelly soil 
will compensate for the lack of water during the month before harvest. 
... A larger amount of water is evidently required if the irrigation is 
deferred until late in the season than in case the water is applied throughout 
a longer period of growth. " There is ample evidence to show that for 
the production of fruits of large size the trees should be well supplied 
with available soil moisture throughout their growing season. Through 
measurements of apples made at intervals of two weeks throughout the 
season it has been found that size increased steadily from the time of 
setting to maturity. 133 This suggests the advisability of cultural treat- 
ments to promote a steady growth. That there is a limit, however, 



72 FUNDAMENTALS OF FRUIT PRODUCTION 

to the increase in fruit size that can be effected through increased 
moisture supply is shown by many irrigation experiments. For instance, 
with peaches on a deep gravelly loam in Utah, it was found that 31 
acre-inches of irrigation water gave as large size and as large yields as 
62 acre-inches under the same conditions. 11 

An interesting moisture relation within the plant itself that often 
affects fruit size is pointed out by Chandler. 34 He shows that the con- 
centration of the sap within the leaves of the tree is higher than that 
within its developing fruits. Consequently in times of drought, when 
the roots are unable to supply the amounts transpired, the leaves actually 
can withdraw moisture from the fruits, even to the point of causing 
wilting while the leaves themselves remain turgid. This not only checks 
temporarily all increase in fruit size but may result in a reduction. Chan- 
dler cites several instances in which, under these extreme conditions, 
more disastrous results occurred in cultivated than in uncultivated 
orchards. Cultivation had been given largely for the purpose of con- 
serving moisture; nevertheless toward the end of a long drought when 
the moisture supply of both cultivated and uncultivated orchards* was 
approaching the wilting coefficient, the trees in the cultivated orchard 
suffered more because they had larger leaf systems and required more 
water to support them. Had summer pruning to reduce the leaf systems 
been done promptly in these cases, evaporation would have been 
reduced and wilting of the fruit prevented. Chandler states, however, 
that summer pruning for the purpose of increasing fruit size through 
reducing leaf area has not been successful. 

Yield. — The increases in yield from an increased moisture supply, up to 
the optimum, are in general still more striking than the increases in size 
because of the indirect effects of moisture through better fruit setting 
and the formation of more fruit buds. 

A striking illustration of the influence of rainfall upon yield is recorded 
for the palm oil tree (Elaeis guineensis) in the British Colony of Lagos. 
Data showing the yearly rainfall and the yearly exports of palm oil and of 
palm kernels are condensed in Table 35. The following quotation fur- 
nishes comment on these data: 

"The yield of fruit from the palm oil tree (Elaeis guineensis) varies according 
to rainfall. With a sufficiency of moisture the tree flowers every five or six weeks, 
and bears eight or nine mature bunches of fruit in the year, but if the rain supply 
is scanty the tree flowers only every ninth or tenth week, and the annual yield 
is reduced to about five bunches. In normal times the Elaeis bears eight heads 
(so-called nuts) in the year, but it follows a similar habit to the cocoanut, the 
heads being formed spirally in the axils of the leaves at regular intervals, which 
are long or short, according as the season is favorable. The mischief arising from 
insufficient rainfall does not finish with the number of heads, for the oil is 
extracted from the fiber of the thin outside layers of the fruit, which are either 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 73 

Table 35. — Yearly Rainfall and Exports of Palm Oil from Lagos 30 



Year 


Rainfall, 


Palm oil, 


Palm kernels, 




inches 


gallons 


tons 


1887 


70.80 
49.87 






1888 


2,446,705 


42,525 


1889 


61.61 


3,349,011 


32,715 


1S90 


90.88 


3,200,824 


38,829 


1891 


64.26 


4,204,835 


42,342 


1892 


69.68 


2,458,260 


32,180 


1893 


82.55 


4,073,055 


51,456 


1894 


70.10 


3,393,533 


53 , 534 


1895 


80.62 


3,826,392 


46,501 


1896 


74.23 


3,154,333 


47,649 


1897 


51.10 


1,858,968 


41,299 


1898 


80.20 


1,889,939 


42,775 


1899 


83.46 


3,292,881 


49,501 


1900 


72.82 


2,977,926 


48,514 


1901 


112.59 


3,304,055 


57,176 


1902 


47.82 


5,240,137 


75,416 


1903 


70.08 


3,174,060 


63,568 



red, ripe, succulent and rich with oil, or starved, yellow, and destitute wholly or 
partially of oil, according to the amount of moisture afforded to the tree during 
the time the fruit has been maturing." 30 Three things are of particular interest 
in connection with the behavior of the palm oil tree in Lagos: (1) Moisture affects 
yield mainly through influencing the frequency of flowering and fruiting. (2) 
The chemical composition of the fruit is greatly modified. (3) Variations in 
rainfall are as likely to influence fruit production the succeeding season as during 
the current year. This is explained by the existence of two seasons of heavy 
rainfall — one early and one late. If the excess or the deficiency is mainly in the 
latter period, its influence is more evident in production the following calendar 
year. More attention is devoted to this phase of the question under Residual 
Effects of Soil Moisture. 

Shape and Color. — The influence of soil moisture on the color and 
shape of fruit is of little importance relatively but it is none the less of 
interest. In Oregon it was found that with the use of increasing amounts 
of irrigation water apples tended to become more angular and elongated 85 
and the same phenomenon has been noted in irrigated orchards in Idaho. 124 
Many observations have indicated that apples in a very dry soil are 
flatter than those of the same variety grown near by but in a somewhat 
better watered medium. In irrigation experiments with peaches in 
Utah, poor color was associated with a small amount of water and high 
coloration with abundant and particularly with late, watering. 11 A 
brighter red color was found on Esopus apples that were well irrigated, as 
compared with a darker and duller red on fruit of the unirrigated or 



74 FUNDAMENTALS OF FRUIT PRODUCTION 

lightly irrigated plots in Oregon. 85 Barss 9 observes that Bartlett pears 
from trees well supplied with moisture are a clear green at picking time; 
those from trees suffering for lack of moisture he describes as bluish-gray 
green. Increased moisture may lead indirectly to poorer color of varieties 
of apples, pears and peaches that have more or less red coloring matter 
in their skin by producing a larger wood and leaf growth and thus 
more shade, the formation of the red pigment in these cases being depen- 
dent upon sunlight reaching the fruit itself. Though this effect of soil 
moisture is noted only late in the season as the fruit is maturing, it is 
not an effect of surplus moisture at that time or just previous, but is 
rather to be attributed to surplus moisture during the spring months 
when most of the shoots and leaves are developed. Thus trees with 
fruits showing the effects of drought in poor size and quality may at the 
same time show the effects of too much moisture during the spring months 
in poor color. Such a condition suggests the contrasting extreme, namely 
high color from good exposure to the light incident to proper foliage and 
shoot development early in the season and good size and quality incident 
to abundant moisture late in the season. Either extreme can be produced 
or at least approximated by skillful culture, particularly in irrigated 
sections where water supply is under control. 

Composition. — That the composition of fruit is influenced materially 
by water supply is suggested by the large percentage of water in the 
tissues of the fruit. It is probable, however, that the most important 
influence of soil moisture upon quality and composition is not in modi- 
fying its water content, but rather in its effect upon other constituents. 
Thus the poor quality of strawberries ripening during or immediately 
after a rainy period is due more to a low sugar than to a high water con- 
tent. Exact figures are not available to show how chemical composition 
of fruits varies with definite changes or variations in soil moisture, con- 
ditions being otherwise the same, but it is presumable that such figures 
would show material differences. Developing oranges may contain 25 to 
30 per cent, less moisture during the middle of the day, when transpi- 
ration is at its highest, than at night when it is at its minimum, 35 but the 
moisture content of apple leaves has been found to vary only from 62.8 
per cent, to 64.8 per cent, when the soil moisture in the plots in which the 
trees were growing ranged from 11 to 24 per cent. 124 This suggests that 
such extreme variations as have been found in the orange are only tempo- 
rary and that the plant possesses a marked ability to construct its 
tissues along a chemical pattern independent of available soil moisture 
to a considerable degree. However, comparatively slight differences in 
chemical composition are often responsible for large differences in flavor 
or quality. In addition, differences in soil moisture may cause slight 
differences in texture and in the size and cohesion of individual cells or 
groups of cells, resulting in great differences in quality. The comparative 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 75 

crispness of fruit grown where there is an abundance of soil moisture is 
a matter of common knowledge. Bartlett pears grown with an extremely- 
limited water supply are distinctly and unpleasantly astringent, though 
fruit of that variety under usual conditions is without astringency. 9 
Peaches supplied early with abundant irrigation water but suffering 
because of its lack late in the season, may be especially sweet and of 
high quality but somewhat shriveled and of little commercial value. 11 

Many claims are made for and against fruits grown in irrigated 
sections. The discussion is based on the assumption that there is some 
more or less direct influence of irrigation water on the composition and 
consequently on flavor and quality. If this were the case the evidence 
would not be conclusive, for fruit raised either in an irrigated or in an 
unirrigated section is a product of the many factors constituting environ- 
ment and not solely of differences in soil moisture. Chemical analyses 
of many hundreds of fruits of different kinds grown with and without 
the use of irrigation water, have led to the conclusion that in most decidu- 
ous fruits differences between those irrigated and those not irrigated are 
negligible. 74 Only in the strawberry were important differences found. 
In that fruit the irrigated berries were lower in dry matter, sugar, acid 
and crude protein and these differences were accompanied by a marked 
difference in keeping quality. There appears to be little reason for the 
popular belief that irrigated fruits as a rule are softer and more watery 
than those not irrigated. It seems to make no difference whether the 
soil receives its water from rains or through an irrigation flume. 

Disease Resistance and Susceptibility. — Correlated with the influence 
of soil moisture on the texture and composition of the tissues of shoot, 
leaf and fruit is its influence on resistance and susceptibility to certain 
diseases. This has been noted many times in the common bacterial 
fireblight of apples and pears. This disease works much more freely in 
soft succulent tissues, slowing up or ceasing entirely as it reaches older 
and harder wood. Thus high moisture content of the soil, forcing a more 
succulent and vigorous growth, favors the development of the disease 
and there are sections where the most practicable method of controlling 
it on certain varieties is such culture as will maintain the soil moisture 
at a point somewhat below the optimum for growth though well above 
the wilting coefficient. An investigation of the relation between water 
content of soil and the prevalence of fireblight in Idaho showed that 
the soil moisture averaged 3 to 8 per cent, higher in badly blighted 
orchards than in nearby orchards having little of the disease. 124 Similar 
differences were found in the soil moisture content of slightly blighted 
and badly blighted parts of the same orchard and in the soil under 
diseased and disease-free trees. Extreme atmospheric humidity may 
occasionally be a contributing factor. Presumably soil moisture exerts 
equally great influence on susceptibility or resistance to many other 



76 FUNDAMENTALS OF FRUIT PRODUCTION 

bacterial and fungous diseases. A series of dry seasons is almost certain 
to be accompanied by an increase in the virulence of the Illinois blister 
canker in those regions where that disease is prevalent. 51 The influence 
of soil moisture on certain physiological disturbances is discussed later. 

Residual Effects of Soil Moisture. — The influence of precipitation or 
of irrigation early during the growing season is more or less immediate. 
On the other hand water falling or applied late during the growing season 
may have less of an immediate effect on the plant and a correspondingly 
greater effect at a later period, or even the following year. Particularly 
is this true of late fall or early winter rains or irrigation. This is due 
partly to the fact that some of the water is stored in the soil for later use 
and partly to the fact that the benefit that the plant derives from absorb- 
ing some of it immediately may not be apparent until considerably later. 
It is thus proper to speak of the residual effects of soil moisture. 

On Vegetative Growth. — It is a common observation that trees suffer- 
ing from drought in late summer and early fall shed their foliage early. 
This is particularly true of species and varieties ripening their fruit 
comparatively early. The function of the foliage during late summer 
and fall is to manufacture food materials which, for the most part, 
are stored through the winter for use in tissue building in the spring. A 
large part of the new growth (roots, shoots, leaves and flowers) in early 
spring is at the expense of stored foods. Premature defoliation, from 
drought or any other cause, therefore, is likely to result in a check to 
growth the following spring through cutting down the available reserves. 
Though exact experimental data in support of this line of reasoning are 
not available there is abundant circumstantial evidence and the record 
of numerous observations is very suggestive. 

Whitten 134 has assembled some data bearing on this question for the 
years 1894-1898 (see Table 36). In commenting on these he says: "It will be 
observed that the last part of the years 1894 and 1897 were marked by severe 
drouths, and that the average growth of uncultivated trees fell off to a marked 
degree during the next year or two after each of these dry seasons. Where 
trees were well cultivated, to conserve the moisture in the soil, this falling off of 
growth was not noticeable. . . . The unfavorable effects of drouth upon 
uncultivated trees may not be so apparent during the dry year itself as it is 1 or 
even 2 years later." Though unfortunately data are not available as to the 
exact moisture content of the soils in these plots during the 5-year period in 
question, there is little doubt about soil moisture being mainly responsible for the 
differences in growth recorded. 

On Yields. — The residual effects of soil moisture are not limited to 
vegetative growth. In all probability they have rather general influence 
and affect yield. This is indicated by investigation of the olive industry 
near Sfax in Northern Africa. 75 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 



77 



Table 36. — Showing Certain Residual Effects of Soil Moisture 

(After Whitten 1 * 4 ) 



Variety 


Age 


Growth (in inches) 


Kind of cultivation 


1895 


f 
1896 1897 1S98 


Ben Davis 

Ben Davis 

Ben Davis 

Jonathan 

Jonathan 

Genet 

Genet 

Genet 


7 
11 
14 

9 
10 
30 

30 
14 


17.6 
12.1 
17.0 
17.2 

7.3 
4.2 

3.6 
13.0 


21.7 
12.4 
9.5 
9.3 
6.6 
6.1 

5.5 
9.3 


23.2 
16.6 
16.2 
13.6 
11.4 
10.4 

8.9 
11.2 


24.5 
14.5 
10.8 
11.0 
9.6 
6.6 

4.4 
7.4 


Clean cultivation. 
Clean cultivation; cover crops. 
Seeded to clover. 

In clover; cultivated under each tree. 
Clean cultivation; cover crops. 
In bluegrass and clover; some culti- 
vation around each tree. 
In bluegrass pasture. 
In clover. 



Rainfall in Inches During the Growing Season for Each of the 5 Years 



Month 



1894 


1895 


1896 


1897 


2.02 


1.04 


3.08 


4.83 


4.33 


6.09 


5.61 


3.19 


3.04 


5.78 


4.33 


6.59 


1.20 


4.93 


3.79 


4.28 


1.29 


2.30 


1.85 


1.89 


7.57 


1.48 


3.61 


0.51 


0.98 


0.25 


2.45 


0.69 



1898 



April 

May 

June 

July 

August . . . 
September 
October. . . 



2.76 
8.39 
9.02 
4.60 
0.47 
5.43 
2.61 



The following quotation illustrates the point: 

"Although the records do not cover a sufficiently long period to establish a 
definite relation, it would appear that there is some connection between the size 
of the crop and the amount of rainfall of the preceding year or years, but not 
that of the spring preceding the ripening of the crop. Thus, the comparatively 
heavy rainfall (3.6 inches above the normal) in 1897 doubtless had something 
to do with the large crop of 1898, although the total rainfall of the first 5 months 
of the latter year was less than half of the normal. Again in 1901, when the 
crop was less than half the average of 9 years, the rainfall for the first 5 months 
was not greatly below the normal, but that of the previous year was less than half 
the normal, and during the 3 years previous the annual rainfall was only a little 
more than half the normal. It is noteworthy that in 1900, after 2 years of 
rainfall much below the normal, the crop was about an average one. This was 
probably due to the heavy rainfall of November, 1899, which was more than three 
times the normal for that month, while the precipitation during the first 5 months 
of the year in which the crop was made was less than 40 per cent, of the normal." 

Still further evidence is furnished by a report on the relation of 
certain climatological factors to fruit production in California: 



78 FUNDAMENTALS OF FRUIT PRODUCTION 

"The character of the autumn, particularly with reference to rainfall, deter- 
mines in large measure the size and the quality of the fruit crop of the following 
year. An interesting example of this relation is apparent in the 1919 deciduous 
fruit crop, which is the largest of this kind ever grown in California. During 
September, 1918, the heaviest rains recorded in a month of September in California 
during 69 years of record were general throughout the central portions of the 
State." 101 

Regularity of bearing, as is pointed out later, is probably more closely 
associated with and dependent upon, natural flowering habit and the 
nutritive conditions within the plant than upon soil moisture. However, 
the following quotation from a report on a series of orchard soil experi- 
ments in Pennsylvania suggests the wisdom of looking after the moisture 
supply when it is more or less under control: "In two treatments, the 
yields of Baldwin and Spy have remained almost constantly between 
400 and 700 bushels per acre annually for the past 7 years, while marked 
fluctuations in yield were occurring in adjacent plots under other treat- 
ments. The essential features of the former treatments have been 
an ample food and moisture supply, the absence of excessive yields in 
any one year, and undisturbed root system." 123 

In most of the cases cited it is impossible to differentiate between the 
direct influence upon the plant of water from the rains of the preceding 
summer and fall stored over winter in the soil and what has been termed 
indirect effects through immediately influencing leaf fall and food storage. 
To the grower it is the combined effect that is important. The facts 
presented carry a particularly significant lesson for the grower in an 
irrigated section where fall and winter rains cannot be depended on, but 
irrigation water is available. They suggest also that the tree that 
matures its crop early in the season, whether a cherry, apricot, peach or 
summer apple, has as real, though perhaps not as great a need of late 
summer, fall and winter irrigation as one maturing its crop in October. 

Influence of Atmospheric Moisture on Growth. — It is difficult in 
many cases to distinguish clearly between the effects of soil moisture and 
of atmospheric humidity on the plant. Atmospheric humidity has an 
influence on plant development independent and distinct from that of 
soil moisture, though it often happens that both influences tend in the 
same general direction. 

In General. — Under average outdoor growing conditions abundant 
soil moisture is likely to be accompanied by relatively high humidity and 
low soil moisture by a dry atmosphere. In practice, therefore, these two 
factors of environment are more or less interdependent. The relation of 
the two is brought out by data presented in Table 37. In a general way 
it may be stated that extreme moisture, either of soil or of air, hinders 
the differentiation of tissues while dryness accentuates the develop- 
ment of strengthening and conducting tissues. Examples of these 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 



79 



Table 37. — The Influence of Moist and Dry Soil and Air on Size of Leaf 

of Tropaeolum Majus 

(After Kohl™) 



Soil 


Aii- 


Relative size of 
leaf blade 


Moist 


Moist 


5 


Moist 


Dry 


4 


Dry 


Moist 


3 


Dry 


Dry 


1 



results are to be found in aquatic plants on the one hand and in desert 
plants on the other. In the former the cuticle is usually thin and per- 
meable, the stomata are numerous and exposed, frequently the surface 
of the epidermis is enlarged and woody tissue, sclerenchyma and col- 
lenchyma are poorly developed. In xerophytic plants, growing under 
very dry conditions, the cuticle is thickened and rendered imperme- 
able by waxy impregnations; the surface of the entire plant is reduced to a 
minimum, the stomata are few in number and frequently situated at the 
base of depressions in the surface of the leaf. Wood and fibers are 
developed to a marked degree and specially differentiated water storage 
tissue is of frequent occurrence. 

Apparently atmospheric humidity, rather than soil moisture, soil, or tempera- 
ture, is the factor determining the limits for the production of certain 
varieties of dates. Those of the Deglet Noor type thrive only in the driest 
climates, like that of the desert oasis with a mean humidity of 35 to 40 per cent. 
Dates of a different type are grown in the vicinity of Alexandria, Egypt, with a 
mean annual humidity of 68 per cent. 92 

Russeting of Fruit. — In addition to the more general influences of 
atmospheric humidity and soil moisture on plant development there 
are certain more or less specific influences on fruits and fruit plants. 
One of the most conspicuous and frequently observed is the effect on the 
russeting of the skin of certain pomaceous fruits, particularly the apple 
and the pear. This results from a cracking and weathering off of the 
epidermis and an increased development of the corky parenchyma 
beneath. It occurs especially in humid climates or during rain}'- sea- 
sons. For instance the Bosc and Winter Nelis pears as grown in the dry 
atmosphere of the Rogue River valley of southern Oregon are practi- 
cally smooth skinned fruits. Grown in the more humid Willamette 
valley a hundred miles farther north their surface is almost completely 
russeted. The Cox Orange apple is a half russet variety as grown in 
England; it is a smooth-skinned fruit as grown in the Okanogan region in 
British Columbia. The fruit trade generally considers that fruit pro- 
duced in irrigated sections has a higher "finish" than fruit of the same 



80 FUNDAMENTALS OF FRUIT PRODUCTION 

varieties produced in non-irrigated orchards. The reason lies in the 
lower atmospheric humidity of the sections where irrigation is practiced 
and is in no way directly connected with the irrigation. 

This russeting of the skin is often attributed to the action of certain spray 
materials and without doubt is sometimes partly or even entirely caused by 
them. In most cases, however, atmospheric humidity is an important contribut- 
ing factor. The following quotation from a report by Morse, 98 who has made a 
study of the subject particularly as it relates to spray injury, is instructive: 

"One of the most prominent facts shown by the tabulated results of 1916 is 
the relatively high per cent, of russeted fruit on each plot, even on the un- 
sprayed check which showed 20.57 per cent. This duplicated a condition which 
prevailed in 1913 when over 31 per cent, of russeted fruit was obtained on the 
plot upon which no insecticide or fungicide was applied, and the different sprays 
produced a corresponding increase in amount. Although this russeting was 
materially increased by different sprays it is evident that much of it must be 
attributed to natural causes. The weather conditions of 1913 and 1916 were 
remarkably similar in many ways, and differed from previous seasons in which 
abnormal fruit russeting did not occur. In 1913 the first spray application was 
followed by a month of unseasonably, cold weather, with frosts and cold, north- 
west winds, associated with much cloudiness and heavy rainfall. In 1916, 
similar conditions prevailed previous to and following the first application. 
This was also followed in 1916 by heavy rains and continuous cloudy weather 
in June after the second application, which was not the case in 1913." 

In extreme cases this russeting may be accompanied by cracking and 
malformation of the fruit, resulting in considerable loss. Sorauer 119 
notes that in the grape similar atmospheric conditions may lead to the 
development of cork pustules on the peduncles or pedicels as well as on 
the fruit. The cork generally starts to develop under the stomata and 
the disorder is likely to make its initial appearance comparatively early. 

Some of the effects of high humidity previously mentioned, for 
example increased leaf surface and the russeting of fruit, are phenomena 
that likewise accompany a decreased light supply. This raises the ques- 
tion as to whether a part of the apparent direct influence of atmospheric 
humidity may not be due in reality to its action in intercepting light. 

Fruit Setting. — Inquiry shows that atmospheric humidity is often of 
greater importance in the setting of fruit than is generally realized. 
Hot drying winds at blossoming time may evaporate the moisture from 
the stigmatic secretions and thus prevent the germination of the pollen. 
Extreme atmospheric humidity may interfere with the work of insects 
in carrying pollen or it may encourage the development of certain fungi 
such as brown rot and apple and pear scab that work on the flowers and 
destroy or injure them. The well known effects of rain during the blos- 
soming season in preventing pollination, in washing away and destroying 
pollen and in diluting stigmatic secretions may be mentioned. A study 



RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 81 

of the "June drop" of the Washington Navel orange in California indi- 
cates that a large part of this drop is due to abnormal water relations 
during that part of the day when transpiration is at its highest. 35 

"During the day the fruits (of the Washington Navel orange) decrease in 
water content as much as 25 to 30 per cent. It has been definitely established 
that under severe conditions when the atmospheric pull is high the leaves actually 
draw water back out of the young fruits to maintain themselves. But this supply 
is not sufficient and they decrease in moisture content also. The combined 
effect of this tremendous loss from leaves and fruits results in tensions in the 
water-conducting systems of the tree. These tensions as well as the water deficits 
have been found to be at their maxima when environmental conditions are most 
severe, that is, between 10 a.m. and 3 p.m. 

"Meteorological records show that the atmospheric humidity of the interior 
valleys is quite low during the growing months, relative humidities of 15 per cent, 
being not uncommon. Such humidities may and do occur without marked 
increase in air temperature. In other words, it is possible for extremely dry 
weather to occur without the characteristic hot-norther. 

"Experiments have been performed in the laboratories at Berkeley in which 
this process of abscission of leaves on cut branches has been induced by artificial 
means. The process itself has been studied and found to consist in the gelatini- 
zation and dissolution of the cell walls resulting in complete separation of the 
cells. ... 

" The major part of the June drop occurs early in the season and has to do with 
blossoms and small fruits. It is caused by a stimulus to abscission arising from 
abnormal water relations within the plant due to peculiar climatic conditions. 

"Further evidence that the cause as indicated is substantially correct lies 
in the fact that in certain orchards which are provided with efficient windbreaks 
and interplanted with alfalfa and heavily irrigated, the water deficits in leaves 
and fruits have been found to be much reduced. Such orchards have less drop 
and are notable for their comparatively large yields. The Kellogg orchard at 
Bakersfield is planted to alfalfa and is shielded by a fairly efficient windbreak. 
Meteorological measurements made in this orchard and on the desert to windward 
show that the climatic complex is greatly ameliorated. . . . The alfalfa tran- 
spires at a tremendous rate and literally bathes the trees in a moist atmosphere. 
The windbreak retards the movement of this relatively moist air away from the 
vicinity. The vaporization of water from soil and plants tends to lower the 
temperature of the air. As the soil is largely shaded, the high soil temperatures 
are reduced, which temperatures operate to cut down root absorption at the time 
of day when water loss from the leaves is greatest. . . . 

" It thus seems probable that under the prevalent practice of clean cultivation, 
during the middle of the day when transpiration is greatest the root absorption 
is actually reduced, resulting in water deficits in all parts of the tree. 

" Not only are clean cultivated orchards subjected to higher soil temperatures, 
but inasmuch as the root system tends constantly toward the surface layers, it is 
much reduced by the annual spring plowing which shears off many of the fibrous 
feeders, thus reducing the root area just before blooming and at the very time 
the trees are under the greatest strain." 35 

6 



82 FUNDAMENTALS OF FRUIT PRODUCTION 

To what extent a very high transpiration may lead to the formation 
of abscission layers and the dropping of fruit in other varieties and in 
other species is not known, but presumably the phenomenon is not 
limited to the Washington Navel orange. On the other hand there is a 
limited amount of experimental evidence showing that very high atmos- 
pheric humidity tends to cause the abscission of partly developed 
apples from the spur. 61 

Summary. — Evidence from both tillage and irrigation experiments 
shows increased vegetative growth, as measured by length of new shoots, 
leaf area and increment in trunk circumference, with increasing moisture 
supply up to a certain limit (the optimum for growth). The amount of 
soil moisture available during the short period of rapid growth in early 
spring is particularly important. When the optimum moisture supply 
is exceeded the correlation becomes negative. Second growth of mid- 
summer and the late summer months is generally associated with an 
irregular moisture supply. An increased moisture supply late in the sea- 
son results in an increase in size of fruit and in larger yields. Regularity 
of bearing is encouraged by an adequate and continuous moisture supply. 
There is a limit, however, to what can be accomplished in this direction 
through increasing soil moisture. In certain species, as the apple, dry 
soil conditions tend to promote an oblate form of fruit. There is no 
very direct relation between moisture supply and fruit color, though 
good moisture conditions tend to yield fruits with brighter colors than 
are obtained from soils that are too dry for best growth and development 
of tree and fruit. The higher colors of fruit from irrigated sections may 
be attributed to more nearly cloudless skies, in comparison with those of 
more humid regions. Fruits that develop where the soil moisture is 
either deficient or in excess are inferior in quality to those developing 
where soil moisture conditions are more nearly normal. Disease suscepti- 
bility is often modified materially by the rate of growth, as influenced 
by soil moisture conditions. The injurious effects of deficient moisture 
supply may be more evident the season following the drought than during 
its occurrence, taking the form of decreased vegetative growth and lowered 
yields. The effects of variations in atmospheric humidity are hardly less 
pronounced than those in soil moisture supply. Russeting of fruit is 
common in many species when the humidity is high. Water deficiencies 
at the time of fruit setting are likely to result in an undue amount of 
dropping. 



CHAPTER VI 

PATHOLOGICAL CONDITIONS ASSOCIATED WITH 
EXCESSES OR DEFICIENCIES IN MOISTURE 

Not only is water a limiting factor to growth, but when there is a 
deficiency or when it is present in excess well defined pathological condi- 
tions may arise. Some of the most difficult disorders with which the 
fruit grower has to deal are to be regarded as drought or as excess moisture 
diseases. 

DISTURBANCES DUE TO MOISTURE EXCESSES 

Excessive moisture conditions are likely to be accompanied by a 
disproportionate development of certain tissues usually parenchyma and 
this is at the expense of conductive tissue. 

The Splitting of Fruit. — One of the most frequent troubles incident to 
the presence of too much water at certain seasons of the year is a splitting 
of the fruit. This is most likely to occur shortly before maturity when 
rains follow a period of drought during which the fruit has been checked 
in its growth. Apparently the checking of growth is accompanied by 
changes in the fruit skin rendering it less elastic so that when growth 
processes are accelerated following a rain it is unable to expand rapidly 
enough to make provision for the developing tissues within. Heavy, 
late irrigation following a long dry season has the same effect. The 
stone fruits are particularly subject to this trouble and certain varieties 
of apples, for example the Stayman Winesap, are likewise susceptible. 
In the stone fruits, splitting is sometimes limited to the stone, the flesh 
and skin remaining intact. Treatment of this trouble, as of most dis- 
turbed conditions due to abnormal water relations, should be preventive 
rather than remedial. Cultural practices should be directed toward 
maintaining in the soil a moderate amount of available moisture so that 
growth will not be checked, even though there may be an extended 
period of dry weather. Splitting of flesh and of stones seldom occurs if 
the tissues of the fruit are kept growing. It is suddenly renewed growth 
following a check that causes the trouble. 

In the fig, splitting may accompany high atmospheric humidity during the 
ripening period even though there be no rain or no sudden changes in water 
content of the soil. However, they are much less likely to split under such con- 
ditions than when rain accompanies a humid atmosphere so that the trees can 
take up an increased amount of moisture. 104 Should dry, warm weather follow 
the splitting of this fruit the fissures may close and partially heal over without 
fermentation setting in. 

83 



84 FUNDAMENTALS OF FRUIT PRODUCTION 

Related to the splitting of the skin and fleshy tissues of many fruits 
and the splitting of the stones of drupaceous fruits is the cracking of 
carpels and seed coats frequently found in apples and occasionally in 
pears and other pomaceous fruits. This is often accompanied by the 
development of a whitish mold-like growth along the edges of the cracks, 
giving rise to a condition spoken of as "tufted" carpels or "tufted" 
seeds. According to Sorauer 116 this condition is due to an excessive 
moisture supply and the consequent disproportionate growth of certain 
cells and tissues. The "tufting" itself is hardly to be regarded as a 
diseased condition, for it is more or less common in certain varieties, but 
apparently an excess of moisture greatly accentuates the condition. It 
in no way injures the quality or value of the apple, except as it provides 
a favorable place for the work of certain fungi which may gain entrance 
to the seed cavity through a broken calyx tube. 

(Edema. — (Edema may be described as a swelling of certain parts 
of a plant caused by a great enlargement of the component cells. In 
extreme cases the cell walls break and the cells collapse, resulting in the 
death of the affected tissues. This condition is due frequently to an 
excess of moisture. It is favored in the case of the tomato by insufficient 
light, too much soil moisture or a soil temperature too high in comparison 
with the air temperature so that transpiration cannot take care of water 
absorption. 5 Sorauer 118 states that in fruit trees these swellings are 
usually covered by cork but that sometimes they break open. He notes 
that the trouble is fairly common when either currants or gooseberries 
are grafted upon the Golden Currant (Ribes aureum). The swellings 
develop just below the union and the cion does not make a satisfactory 
growth. In this case the excess of water is to be regarded as a local 
rather than a general condition. 

A similar disorder in which the bark develops at the expense of the 
wood, has been described in the pear, under the name "parenchyma- 
tosis." 118 The swellings may be on one side only of the limb or trunk or 
they may extend around it, giving rise to a barrel shaped or cylindrical 
enlargement, which may be accompanied by a splitting of the bark. 

There has been described a disorder of the grape also, more or less 
closely related to oedema, due to excessive atmospheric humidity. It is 
most frequently found in grapes grown under glass. On the leaves and 
peduncles intumescences develop which are characterized by great 
turgidity, a high oxalic acid and low starch content. 120 

Fasciation and Phyllody. — Fasciation, or the production of a flat 
branch which resembles several branches grown together is regarded 
generally as a malformation belonging in the field of teratology rather 
than as a pathological or diseased condition induced by agencies more or 
less under control. Sorauer, 117 however, places it among the distur- 
bances due to overfeeding and associated with excessive water supply. 



PATHOLOGICAL CONDITIONS 85 

A form of phyllody, known as "false-blossom" or "Wisconsin false- 
blossom," apparently caused by an excessive water supply has been 
observed in some of the cranberry bogs of the Northern states. It is 
characterized by more or less leaf-like calyx lobes and petals, aborted 
or malformed pistils and stamens, the production of little or no fruit and 
an appearance of the plant suggestive of witches' broom. The trouble 
"is usually associated with extreme wet or dry conditions of the bog, 
but most frequently with an excessive water supply. In most of the 
localities in which it has been observed the affected plants were growing 
in a deep, coarse peat soil having an excessive water supply during the 
greater part of the growing season." 110 What is evidently a very similar 
disorder, often caused by disturbed water relations, has been described 
under the name "virescence" as affecting the coffee tree in Indo-China. 39 

Chlorosis. — Chlorosis in plants is generally associated with some form 
of malnutrition and some attention is devoted to it in that connection. 
However, Taylor and Downing 124 found it accompanying over-irrigation 
in a number of Idaho apple orchards. Indeed they came to regard it as 
one of the evidences of excessive applications of irrigation water. It is 
possible that the chlorotic condition of the trees was induced through 
some influence of the excess water supply on the plant nutrients in the 
soil or the foods in the plant, but directly or indirectly the surplus 
moisture was responsible for it. A chlorotic condition of the peach 
induced by over-irrigation has been reported in Baluchistan. 70 Its early 
symptoms were much like those of the "peach yellows" of the eastern 
United States and at one time it was thought to be that disease. It was 
accompanied often by much gumming and unless promptly treated the 
tree died. The use of less irrigation water and the employment of cultural 
practices leading to a better aeration of the soil were efficient correc- 
tives. Chlorosis has been found in heavily watered seed beds of the 
western pine in Nebraska while check plots showed none. 81 

Rough Bark or Scaly Bark Disease. — This disease according to 
Sorauer 11 results in a scaling off of the bark from the roots and to a less 
extent from the stem. It has been described as affecting the apple, 
cherry and plum when growing on low, wet ground. When appearing 
on the roots it is likely to cause the death of the tree; when it attacks 
the trunk it is less serious. Histologically what takes place is an excessive 
lengthening of some of the bark cells. This process may continue deep 
into the bark layer and interfere with normal functions at the diseased 
spot. 

Watercore. — Curiously enough it is sometimes difficult to decide 
whether a certain disturbance is due to drought or to an excess of mois- 
ture. The temporary rising of the ground water table may result in 
the death of a considerable part of the root system. Later, with lowering 
of the waier table the soil dries out and if there is a prolonged dry period, 



86 FUNDAMENTALS OF FRUIT PRODUCTION 

the tree with its reduced root system may suffer for lack of water and 
drought injury ensue. It is a case of drought injury but in the last 
analysis excess soil moisture at another season is the real determining 
factor. It is likewise a paradox that some forms of watercore must be 
regarded as due to drought. Though many cases are to be attributed to 
other factors, Sorauer 115 describes at least one form as associated with a 
deficient soil moisture supply. In this form, water fills the intercellular 
spaces and the affected tissues become hard and glassy. The outer 
portion of the fruit is involved more directly than the tissues immediately 
surrounding the core. The seeds remain white and do not ripen and the 
affected fleshy tissues turn dark upon exposure to air more rapidly than 
normal tissues. They have less dry matter, less ash and less acid. 
Zurich Transparent, Gloria Mundi, White Astrachan and Virginia 
Summer Rose are mentioned as varieties particularly susceptible to this 
disease. 

The watercore more frequently occurring in the United States is 
found in the core of the fruit and in the region of the main vascular 
bundles, though it not infrequently extends to the surface or may be 
limited even to the surface layers. This form of watercore is particularly 
virulent in regions of intense sunlight and abundant soil moisture. 
Tompkins King, Fall Pippin, Yellow Transparent, Early Harvest, 
Rambo and Winesap are mentioned as particularly susceptible varieties. 26 

DISTURBANCES DUE TO MOISTURE DEFICIENCIES 

A deficiency in the water supply is likely to be accompanied by dis- 
turbances in the conductive system and an excessive development of 
stone cells and strengthening tissue. 

Defoliation. Premature Ripening of Wood. — Summer drought often 
leads to premature ripening of the fruit, early leaf fall and premature 
entrance into the winter rest period. Frequently the attacks of certain 
fungi hasten these processes so that distinction between their influence 
and that of drought is difficult; nevertheless there can be no doubt that a 
lack of available moisture has an important influence of this kind. These 
effects of drought are manifest in various ways in the different fruits. 
For instance, the leaves of the peach and cherry turn yellow and fall, 
those of the grape turn yellow or red at the edges or between the veins 
and those of the pear do not become yellow but appear brown or burned 
in spots and remain clinging to the trees. 114 When yellowing is due to 
drought injury it is as a rule those parts of the leaf farthest removed from 
the veins that yellow first. A somewhat unusual form of defoliation due 
to a drought has been mentioned as a pectin disease. 114 It has been 
observed on the grape and consists in the formation of an abscission layer 
between the leaf blade and petiole, resulting in the premature falling of 
the blade. The loss of leaves from drought robs the plant of essential 



PATHOLOGICAL CONDITIONS 



87 



mineral matter, particularly nitrogen and may interfere in this way with 
its nutrition as well as through reducing the manufacture and storage of 
elaborated organic materials. Table 38 shows the mineral constituents 
of Syringa leaves at the time of defoliation from drought and at the time 
of normal abscission. The yellowing and dropping of the leaves of 
dwarf pear trees in times of drought while those of standard trees remain 
normal is clear evidence that the trouble is due mainly to a lack of 
moisture, the limited root system of the quince being unable to supply 
the requirements of the cion in such emergencies. 114 



Table 38. — Mineral Constituents op Syringa Leaves at Different Periods 
in Percentages of Dry Weight 

(After Sorauer 114 ) 



When defoliated by 
summer drought 



When normally drop- 
ping in the fall 



Nitrogen 

Phosphoric acid 

Potash 

Calcium oxid. . . 
Ash 



1.847 
0.522 

2.998 
1.878 
8.028 



1.370 
0.373 
3.831 
2.416 
9.636 



Apparently related to these troubles induced by drought is the tip- 
burn of certain plants occurring during periods of very high transpiration. 
Even a few hours of very rapid transpiration in intense sunlight, high 
temperature and low atmospheric humidity may lead to so great a reduc- 
tion of the water content in the edges of the leaves of the potato that 
recovery of turgidity is impossible. 88 The affected tissues die, a condition 
known as tip-burn. 

Another closely related form of drought injury has been found on the 
grape in New York. It is perhaps best described in the words of the 
original report : 

"Vines affected with the trouble first show a streaked pallidness of the 
leaves in the intervascular spaces. Later these streaked areas become yellow. 
The discoloration is more marked near the margins and eventually the pallid 
areas coalesce and form a yellowed band extending around the margin. As the 
season advances this band dies and becomes functionless. Isolated areas of the 
leaf blade deaden and when these join, a considerable part of the leaf tissue may 
become functionless. When the entire leaf is affected the outer margin often 
curls upward. The injury is cumulative unless favorable conditions are estab- 
lished in the succeeding years, i.e., optimum rainfall, etc. As a result of the 
injury to the foliage, growth is materially checked and the wood usually fails to 
mature well. The fruit does not color nor is the normal amount of sugar fixed. 
'Shelling' may result. 



88 FUNDAMENTALS OF FRUIT PRODUCTION 

"Considering the facts at hand it would seem that a lack of available soil 
moisture, at critical periods in the vine's growth, or a lack of root aeration as a 
result of the impervious subsoil together with the shallow depth of surface soil, 
are the principal contributing factors to the affection. With this soil type the 
sickness is at its height in seasons of drought as well as in those of excessive 
rainfall. Soils such as the yellow silt are generally deficient in organic matter, 
and hence in their water-holding capacity. With them the affection is worst in 
seasons of drouth and least in those of normal rainfall. During early summer the 
vine makes a rapid growth of succulent shoots and leaves which require large 
amounts of water to develop." 50 Newly planted vineyards, where the vines 
do not yet have extensive root systems, are more likely to be affected. 

Dieback. — From the form of drought injury described in the grape, 
it is but a step to more serious conditions resulting in the death of 
some of the twigs, shoots or branches of the tree. This may occur in 
trees of almost any kind, the symptoms varying somewhat in different 
species. However, there is no mistaking the disease when it is present- 
Without doubt dieback may be due to any one of a number of factors. 
Chief among these is an inadequate water supply, not necessarily at the 
time the symptoms are first noticed, but perhaps many months earlier. 
Batchelor and Reed 12 have described dieback as it occurs on the English 
walnut. Since its appearance there is fairly typical of its occurrence on 
many other fruit trees the following account is taken from their report: 

"We have very convincing evidence to show that trees which enter the 
dormant period in the fall in a» perfectly normal and healthy condition may 
suffer from dieback due primarily to a lack of sufficient soil moisture during the 
winter months. During the winter, trees give off moisture through the limbs 
and twigs. If for a prolonged period there is not enough soil moisture available 
to the roots, the trees are unable to obtain sufficient water to offset the loss by 
evaporation from the branches. In that case young branches, the thin bark of 
which permits rapid loss of water from the wood, may die as a result of desic- 
cation. This injury is first evident when such branches fail to produce new growth 
the following spring. . . . Frost injury is usually confined to 1-or 2-year old 
wood, but winter drought may kill back limbs 8 years old. 

"Another condition which is equally critical and apt to injure bearing trees, 
as well as young ones, is the occurrence of a fluctuating water-table. The sudden 
rise of a fluctuating water-table kills that portion of the root system which is 
located in the saturated stratum. In severe cases where the major portion of the 
root system is killed the twigs and young limbs of the tree later exhibit typical 
cases of 'dieback.' It might seem paradoxical that the top of the tree should dry 
out and die when the roots stand in an excessively wet soil, but there is nothing 
contradictory in the situation when it is seen that the death of the major portion 
of the roots makes it impossible for the top to receive the necessary moisture to 
sustain life." 

Though much of the. dieback or exanthema found in citrus trees is 
due to disturbed conditions of nutrition there seems to be no doubt that 



PATHOLOGICAL CONDITIONS 89 

the disease is generally associated with abnormal moisture conditions. 
Trees subject to poor drainage, underlaid with hardpan or subject 
during the previous season to extreme drought or to an irregular water 
supply are most subject to the disease. 49 Drought, therefore, must be 
regarded as an important contributing factor. Other than the dying 
back of the limbs, this disease presents a number of well defined symptoms 
in citrus trees that may be mentioned as further illustrations of the dis- 
turbed and pathological conditions which may arise from, or be end 
products of, an abnormal water supply. Among them are: the produc- 
tion of gum pockets, stained terminal branches, ammoniated fruits, bark 
excresences, multiple buds, exceptionally deep green color of the foliage, 
the production of S-shaped terminal shoots and of coarse leaves somewhat 
like those of the peach in shape. 49 

Cork, Drought Spot and Related Diseases. — Under these names have 
been described numerous disorders of fruit trees that are apparently 
related. Indeed differentiation between them is frequently difficult, if 
not impossible. This is understood easily because they are in fact 
closely related and are perhaps only different symptoms of the same 
fundamental disturbance in the physiology of the plant. The following 
descriptions are from the reports of those who have made a close study 
of them. 

Fruit-pit. — " In the early stages of fruit-pit one finds numerous sunken areas 
from 2 to 6 millimeters in diameter on the surface of the apple. These 
depressions are somewhat hemispherical in shape and have the appearance of 
bruises. At this stage the spots are not brown and often show no difference in 
color from the surrounding surface of the apple. . . . Later they begin to take 
on a brown tint, but at first this seems to show through from rather deeply 
seated tissue and not to arise from any discoloration of the epidermal or imme- 
diately underlying cells. Sections of such spots show that this is the case, and that 
the browning and shrinking of the cells occur in the pulp of the fruit and in the 
tissue that is transitional between it and the hypodermal parenchyma. . . . 
Later the surface cells also become dark brown. ... As the disease advances 
spots situated near each other often become confluent, developing into one large 
spot. In all such cases examined it was found that the original spots were 
closely connected with one vascular branch. . . . The surface spotting is often 
accompanied by browning of the tissue immediately surrounding the vascular 
bundles. Upon cutting such an apple one sees numerous apparently isolated 
brown spots. Further study shows that these are not isolated but are in reality 
continuous strands of brown tissue surrounding the vascular bundles. The 
portion of the vascular system that is most commonly affected is that lying 
within fifteen millimeters of the surface of the apple. The surface spots often 
occur without the internal browning and also the internal browning may occur 
unaccompanied by any surface derangement." 24 

Cork. — Cork is most commonly observed when the apple is anywhere from 
half grown to nearly mature. It may be briefly characterized as internal brown- 



90 FUNDAMENTALS OF FRUIT PRODUCTION 

ing, described by Brooks in the preceding paragraph, but without external pits 
and with the surface of the apple thrown into a series of elevations and depres- 
sions. A large number of brown corky areas occur throughout the flesh, follow- 
ing closely the course of the vascular bundles. In no case do these extend 
outward as far as the skin, consequently there are no external brown pits charac- 
teristic of true fruit-pit or stippen. A further difference from the usual type 
of fruit-pit is that the spots are not more abundant in the peripheral zone, but 
are scattered throughout the flesh of the fruit. There is no bitter taste connected 
with this disease in Fameuse apples. 97 

"Under the microscope the internal brown spots of cork appear as aggrega- 
tions of cells with brown shrunken contents. A number of the cells, though not 
all, are shrunken and collapsed. Around the corky portion the healthy cortex 
cells form a ladder-like arrangement of smaller, more nearly rectangular cells. 
It is as though they had been stimulated to rapid division in response to the 
decreased pressure from the direction of the diseased area. Outside of this zone 
the pulp cells are normal in size and form. The close relation of the dead spots 
to the vascular system is very evident under the microscope." 97 

Surface Drought Spot. — "An early stage of the disease is manifested by an 
irregular light-brown area in the skin. When the fruits affected are large, two 
or three centimeters in transverse diameter, the surface of the fruit is usually 
smooth and regular, there is no shrinkage or sinking in, nor any abnormality 
in the flesh beneath. . . . When the spot first appears tiny drops of a clear or 
yellowish gummy exudate may occur on its surface. Under the microscope this 
exudate shows as a clear gum. ... It is considered to be merely an expression 
of cell sap from the diseased hypodermal cells. . . . Most of the fruits 
affected when young drop from the tree. Some of them . . . persist, and as 
they grow the affected areas become roughened and cracked." 97 

Deep-seated Drought Spot. — "This type of lesion is characterized by the 
presence of brown, corky areas in the flesh of the apple and by a sinking in of 
portions of the epidermis. On young fruits, from 1 to 2 or 2)4, centimeters in 
transverse diameter, the disease appears as a large brownish area in the skin of the 
fruit, usually near the blossom end, which is irregularly sunken and wrinkled, 
indicating shrinkage of the tissues beneath. Cross-sections show brown areas 
in the flesh near the periphery. These are opposite the main vasculars, and often 
in the center of one of them there is a large cavity, the apex of which reaches one of 
these vessels. (Occasionally, apples are found in which there is one of these 
corky areas or cavities opposite each of the 10 main vasculars.) These internal 
spots are often connected by a narrow brown streak running close to the periphery 
of the apple. Sometimes these streaks do not connect, but extend only a short 
distance in either direction from the central spot. The shrinkage of the skin 
over a considerable area, and the presence of these brown corky spots and streaks 
in the periphery, suggest the type of fruit-pit described by McAlpine as 'con- 
fluent bitter-pit' or 'crinkle.' . . . Microscopically, sections of the diseased 
spots show that the trouble is confined to two or three layers of the hypodermal 
parenchyma, usually the inner layers, though sometimes the entire hypodermis is 
affected and a few dead cells are also found in the flesh. The diseased 
cells retain their normal outline, but their contents have become brown and 
amorphous." 97 



PATHOLOGICAL CONDITIONS 91 

Dieback and Rosette. — Dieback in its early stages appears usually in the 
spring. Some or all of the buds toward the ends of the shoots remain dormant, 
while lower buds start. The shoot ends that do not vegetate may remain alive 
all season or they may dry out and die earlier. "The appearance of one of these 
dieback shoots the following summer was that of a completely dead tip from 
6 inches to 1 foot long, often with a distinct marginal crack between it and the 
living part below. From some point back of this tip a healthy lateral developed 
to renew the branch." 97 

The early stages of dieback may be observed in cross sections of dieback 
twigs of the current season's growth. "Such a twig usually shows entirely dead 
tissue near its tip and a discoloration in the cambial area running back for a 
variable distance. Under the microscope this discolored zone shows, if the 
sections are taken near the tip, a large number of cells with browned contents in 
the cambium, phloem and pericycle. If sections are made from parts of the 
twig a short distance below, it will be seen that growth has been made subsequent 
to the injury. The injured cambium has produced a quantity of the so-called 
parenchyma wood, the browned cells of the phloem and pericycle being pushed 
outward. Finally, the parenchyma zone becomes buried by a layer of new 
xylem, outside of which are found normal bark and cambium." . . . Often 
some of the buds on the lower part of such dieback shoots "developed clusters 
of very small, lanceolate leaves with shortened petioles. In some cases the twigs 
made a very short terminal growth, resulting in a thickened, shortened axis an 
inch or so long, bearing a cluster of leaves, some normal and some short lanceolate, 
the general effect being that of a long bare twig capped by a rosette of leaves." 97 

In commenting on these diseases Mix remarks: "It is evident that we have 
under consideration, not two distinct apple diseases, but at the most, two types 
of the same disease: (a) Drouth spot, with which are associated abnormalities 
of the foliage, called drouth dieback and drouth rosette; and (b) cork, which 
may occur in association with drouth spot, but which often occurs independently, 
and is then not associated, except rarely, with any disease of the foliage. 

"The writer's observations show that these diseases may occur in both wet and 
dry seasons. There is, however, a marked relation of weather conditions to the 
disease. They tend to disappear during wet weather and are much more serious 
during a dry period, especially dry weather occurring early in the season. 

"Since, however, in a wet season, and under conditions where there seems to 
be no deficiency of moisture, these diseases may occur in trees that have been 
previously diseased year after year, insufficient soil moisture cannot be looked 
upon as the sole cause. . . . 

"It is suggested that the exact manner of occurrence of the injury may be 
by the leaves robbing the fruit of water during a critical period Of low root supply 
and high transpiration. Rapid wilting of the fruits can be brought about by 
excessive transpiration from the leaves. It has been seen that this wilting may 
result in the death of certain cells near the vascular bundles, forming lesions 
resembling those of drouth spot, and occasionally, of cork. Chandler has pre- 
sented evidence that transpiration from the leaves may bring about a scarcity of 
water in the fruit under field conditions. It is not impossible that this is at least 
one of the ways in which the disease may be caused. 

"This seems more likely than that injury is due to an excessive transpira- 



92 FUNDAMENTALS OF FRUIT PRODUCTION 

tion from the fruit itself, or, as suggested by McAlpine for 'crinkle,' to the failure 
of the vascular network over large areas. The striking thing about these diseases 
is the presence, not the absence, of meshes of this vascular network in close 
proximity to the dead cell areas. 

"In making the above suggestion as to the cause of cork and drouth spot, the 
writer realizes that the small amount of experimental work done does not warrant 
a definite conclusion. There is, undoubtedly, much yet to be learned of the 
real nature of these diseases. 

"Furthermore, it is not intended to advance this theory to explain the cause 
of true fruit-pit, or stippen, which occurs in a late stage of the fruit's growth and 
is said to develop in storage." 

The findings of Brooks and Fisher, 25 who also made an extended study 
of drought spot and cork in apples, in the main corroborate the conclusions 
of Mix just quoted. They succeeded in producing drought spot experi- 
mentally by subjecting Winesap trees to a sudden and severe drought 
when the fruit was about 1 inch in diameter. Furthermore, trees of 
other varieties accidentally receiving similar treatment through mishaps 
to the irrigation system produced fruits exhibiting the same condition. 
It was noted in the course of the investigation that many trees after once 
producing drought spot fruits continued to bear them in later years, 
even though suitable soil moisture conditions were provided. This the 
investigators believed to be due to the loss of many roots when the 
drought occurred. They found cork, or troubles very similar to it, in 
many of the apple producing sections of the Pacific Northwest and in 
New York, Virginia and West Virginia. In summarizing their findings 
they state : 

"In nearly every case where the disease has been observed either in the 
East or West, its occurrence in the orchard has been closely correlated with certain 
peculiar soil conditions ; sometimes an excess of alkali or an out-cropping of slate, 
but more often a shallowness or openness of the soil. In most sections cork 
has been most serious when there was a .shortage in soil-water supply, either 
resulting from light rainfall or a lack of irrigation. 

"The observations reported above seem to indicate that cork is a form of 
drouth injury; yet the disease appears to differ from typical drouth spot, both 
in characteristics and conditions of occurrences. With certain varieties of 
apples drouth spot can apparently be produced on any soil under conditions of 
sudden and extreme drouth. Cork seems to be the result of a less severe but 
more chronic drouth on trees located on certain peculiar soils, especially on soils 
that are lacking in humus and are not retentive of moisture. Blister is closely 
associated with cork and is probably produced by the same agencies. 

"It should be noted in this connection that the harmful effects of drouth are 
not always in proportion to the degree of desiccation. Other factors must be 
considered in a study of drouth troubles, and among these are the percentage 
of harmful substances in the soil water and the general growth condition of the 
plant." 25 



PATHOLOGICAL CONDITIONS 93 

In the pecan there is a related disorder, though its most conspicuous 
symptom is the appearance of rosetted branches. This is associated with 
a deficiency of humus as well as an insufficient moisture supply in the soil 
but destruction of roots through drought or an extreme depletion of the 
soil moisture are important contributing factors. 96 

Bitter-pit. — In bitter-pit "the diseased tissue is dry and spongy, the cells are 
collapsed but still full of starch, and the cell walls show no sign of thickening or 
disintegration. . . . The pits are usually associated with the terminal branches 
of the vascular bundles, and the surface spotting is often accompanied by a 
browning of the vascular tissue deeper in the fruit, giving the appearance of nu- 
merous brown spots in the flesh when the apple is cut. . . . 

"The results of the various experiments have been uniformly consistent in 
showing that heavy irrigation favors the development of bitter-pit. Heavy 
irrigation throughout the season has given less of the disease than medium irri- 
gation followed by heavy, and light irrigation throughout the season has resulted 
in more bitter-pit than heavy irrigation followed by light. Heavy irrigation the 
first half of the season caused the trees to develop a more luxuriant foliage and 
probably produced a lower concentration of cell sap in the apples, both of which 
facts would tend to make the fruit less susceptible to the forcing effects of late 
irrigation. The amount of irrigation in August and September has apparently 
largely determined the amount of disease. 

"Sudden changes in the amount of soil water do not appear to have had any 
effect upon the amount of disease. No evidence has been found that bitter-pit 
is brought about by a rupture or bursting of the cells. 

"Large apples have been more susceptible to bitter-pit than small ones, but 
the increase in the disease from heavy irrigation has been almost as great on the 
small and medium sized fruits as on the large. . . . Apparently apples are not 
susceptible to bitter-pit merely because they are large, but rather because of 
conditions that may sometimes accompany an increased growth. 

"The results as a whole point to the harmful effects of heavy late irrigation 
regardless of the size of the fruit. In looking for the final cause of the disease not 
only the direct growth-forcing effects of the water should be considered but also 
the effects of the excess water upon the soil flora and soil solutes." 25 

Jonathan-spot. — " 'Jonathan-spot' is the term applied to superficial black or 
brown spots that are especially common on Jonathan apples. ... In the early 
stages of the disease only the surface color-bearing cells are involved and the 
spots are seldom more than 2 mm. in diameter, but later the spots may enlarge 
to a diameter of 3 to 5 mm., become slightly sunken and spread down into the 
tissue of the apple to a considerable depth. . . . The results of both years 
gave some evidence that heavy irigation was more favorable to the disease than 
light irrigation, but there was nothing to indicate that the amount of soil moisture 
was an important factor in determining the amount of Jonathan spot." 25 

To what extent these, or similar diseases are to be found in other 
fruits is unknown. There is reason to believe, however, that just as some 
of these diseases of the apple have been dismissed as winter injury or as 



94 FUNDAMENTALS OF FRUIT PRODUCTION 

some other rather obscure disorder, so some of the serious troubles of these 
other fruits may prove eventually to be due directly or indirectly to 
drought. Rosette and little-leaf are certainly not unknown in the cherry, 
apricot, plum and pear though little attention has been devoted to them. 

Barss 10 records "cork" as of frequent occurrence in pears in Oregon and a 
" drought spot " or " gum-spot " as not uncommon in prunes. Both are attributed 
to disturbed water relations. In speaking of the gum-spot of prunes he says: 
"It comes on just about in midseason and appears first as watery-looking spots 
on the fruit. These usually swell and burst open by a crescent-shaped slit, from 
which there is an exudation of transparent gum that hardens on the surface. In 
the flesh of such prunes small brown flecks always appear, beneath the gum- 
spot. These usually consist of a few dead pulp cells situated in the region of the 
outer network of veins. Such injury is often slight and the prunes mature with 
very little evidence of the trouble. More severe injury, however, may result in 
the death of larger areas of the pulp. The resulting collapse of the tissues and 
cessation of growth produces an irregular or corrugated surface. Such affected 
prunes usually color up prematurely and drop off. 

"In some years, as the prunes approach maturity great losses to growers 
result from an internal breaking down of the flesh, with brown discoloration and 
disagreeable odor, which has sometimes been erroneously mistaken for brown 
rot. This internal browning usually starts immediately around the pit, but often 
extends outward until in some cases it reaches the skin and involves the whole 
flesh. The trouble is . . . presumably due to disturbed water balance in 
the tree and perhaps is similar in origin to 'punk' in the apple." 

The assumption should not be made, however, that all these diseases 
described and discussed here under the names of cork, fruit-pit, bitter- 
pit, Jonathan-spot, dieback, rosette, etc. are always due exclusively to 
disturbed water relations. Though without doubt they often are caused 
directly or indirectly by excessive moisture or by drought, there are 
other contributing factors and in some instances their occurrence 
may be due to these other factors alone. For instance, White 132 and 
Ewert 47 ' 48 present evidence that in Australia much of the bitter-pit in the 
apple is due to localized poisoning caused by the presence of minute 
quantities of certain mineral toxins absorbed either from the soil or from 
the coating of certain spray materials on the fruit itself. 

Black-end. — Under the name black-end has been described a physiological 
disease of pears in which the skin around the apical end of the fruit turns black 
while the flesh immediately underneath becomes hard and dry and may crack. 10 
Such fruits are likely to be rounded at the apical end instead of depressed in the 
usual manner. The blackened area often blends gradually into healthy tissue. 
This disease is found most frequently in the hotter and drier portions of Oregon, 
and "all the circumstantial evidence points to the probability that excessive 
evaporation in hot weather or insufficient soil moisture are responsible for its 
development, since it appears usually on soils either unfavorable for root 
growth or unretentive of moisture or both." 



PATHOLOGICAL CONDITIONS 95 

Silver Leaf. — Sorauer 114 describes one type of silver leaf occurring 
on apricots, plums, cherries and apples. The immediate cause of the 
silvery or milky appearance of the leaves is the partial separation of the 
epidermal cells from one another and from the palisade cells, the inter- 
cellular spaces becoming greatly enlarged. The older leaves are more 
subject than the younger. This disease is usually associated with some 
gummosis of the limbs and in aggravated cases the affected branches die. 
Aderhold suggests that the failure of the middle lamella to cement 
adjoining cells is due to a lack of calcium, which permits the pectin to 
become soluble. As the disease generally occurs locally in the plant, 
the lack of calcium is not the result of a deficiency in the soil but is due 
to a local disturbance in the conducting system. 

Some other forms of silver leaf occasionally appearing in the orchard 
and affecting entire trees or entire orchards may be due to quite different 
causes. 

Lithiasis. — Drought at or shortly before the maturing season of pears 
has been noted often to cause increased grittiness of the flesh, the stony 
aggregations around the core becoming larger. Sorauer 112 describes an 
aggravated form of this trouble under the name lithiasis. In this drought 
disease sclerotic tissue develops near the surface of the fruit, particularly 
on the sunny side. Ordinarily it is found only in cases of extreme 
drought. 

Summary . — Either an excess or a deficiency in soil moisture is likely 
to be accompanied by a disturbed condition within the plant and often 
by the appearance of some pathological symptom. Among those brought 
on by excesses in the moisture supply are fruit splitting, fasciation, phyl- 
lody, cedema, chlorosis, scaly bark and water core. High atmospheric 
humidity is an important contributing factor in cedema; fruit splitting 
is due to an irregular soil moisture supply as much as to an excess. 
Measures against all of these troubles should be preventive rather than 
remedial. They include provision for adequate drainage and caution 
in the use of irrigation water. Premature defoliation and the attend- 
ant ripening of the wood is one of the more serious results of a moisture 
deficiency. It is likely to be followed by decreased vegetative growth, 
lessened yields and in extreme cases, dieback. The earlier entrance 
into the rest period and the poorer maturity of the wood both tend 
toward susceptibility to winter injury. Dieback, rosette and little- 
leaf are closely related disorders of the tree due in many cases to summer 
drought. Often associated with these tree diseases, but sometimes more 
or less independent of them, are a number of closely related diseases of the 
fruit itself that have been described under the names: fruit-pit, cork, 
drought spot, bitter-pit, Baldwin-spot, Jonathan-spot and black-end. 
It is probable that some of these terms as commonly used refer to one and 
the same trouble, or at least they overlap. This group of disorders, 



96 FUNDAMENTALS OF FRUIT PRODUCTION 

though directly due to drought, frequently may be a result of too much 
moisture, or a water table too high at some other season, resulting in a 
restricted root system. Here again, protection lies more in preventive 
than in remedial treatments. 

Suggested Collateral Readings 

1. Schimper, A. F. W. Plant Geography. (English Translation) Oxford, 1903. 

(Particularly pp. 159-173, 81-85.) 

2. Bowman, I. Forest Physiography. New York, 1914. (Chapter 3 on Water 

Supply of Soils; Relation to Plant Growth and Distribution, pp. 41-54.) 

3. Weaver, J. E. The Ecological Relations of Roots. Pub. 286 Carnegie Inst, of 

Washington. 1919. (Particularly pp. 27-28, 100-108, 121-127.) 

4. Hilgard, E. W., and Loughridge, R. H. Endurance of Drought in Soils of the 

Arid Region. Rept. Cal. Agr. Exp. Sta. for 1897-8. Pp. 40-64. 

5. Loughridge, R. H. Moisture in California Soils During the Dry Season of 1898. 

Rept. Cal. Agr. Exp. Sta. for 1897-8. Pp. 65-96. 

6. Mason, S. C. Drought Resistance of the Olive in the Southwestern States. 

U. S. D. A., Bur. PI. Ind. Bui. 192, pp. 9-33. 1911. 

7. Huntington, E., and others. The Climatic Factor as Illustrated in Arid America. 

Pub. Carnegie Inst, of Washington, pp. 101-174. 1914. 

8. Whitten, J. C. An Investigation in Transplanting. Mo. Agr. Exp. Sta. Res. 

Bui. 33. 1919. 

9. Bates, C. G. Windbreaks; Their Influence and Use. U. S. D. A., Forest Service 

Bui. 86. 1911. 

10. Gourley, J. H. Some Observations on the Growth of Apple Trees. N. H. 

Agr. Exp. Sta. Tech. Bui. 12. 1917. 

11. Green, W. J., and Ballou, F. H. Orchard Culture. Ohio Agr. Exp. Sta. Bui. 171. 

1906. 

12. Hedrick, U. P. A Comparison of Tillage and Sod Mulch in an Apple Orchard. 

N. Y. Agr. Exp. Sta. Bui. 314. 1909. 

13. Hedrick, U. P. Tillage and Sod Mulch in the Hitchings Orchard. N. Y. Agr. 

Exp. Sta. Bui. 375. 1914. 

14. Mix, A. J. Cork, Drouth Spot and Related Diseases of the Apple. N. Y. Agr. 

Exp. Sta. Bui. 426. 1916. 

15. Gladwin, F. E. A Non-parasitic Malady of the Vine. N. Y. Agr. Exp. Sta. 

Bui. 499. 1918. 

16. Briggs, L. J., and Shantz, H. L. The Water Requirement of Plants. A Review 

of Literature. U. S. D. A., Bur. PI. Ind. Bui. 285. 1913. 

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54. Green, W. J., and Ballou, F. H. Ohio Agr. Exp. Sta. Bui. 171. 1906. 



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64. Ibid. P. 200. 

65. Ibid. P. 263. 

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1897-8. 

67. Hooker, H. D., Jr. Ann. of Bot. 29: 265-283. 1915. 

68. Hooker, H. D., Jr. Mo. Agr. Exp. Sta. Research Bui. 40. 1920. 

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72. Huntington, E. The Climatic Factor as Illustrated in Arid America. Pp. 

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73. Jones, F. R. A Study of the Development and Extent of the Roots of Apple 

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78. Ibid. P. 189. 

79. King, F. H. U. S. D. A., Bur. Soils Bui. 26. 1905. 

80. Kohl, F. G. Die Transpiration der Pfanzen. Brunswick, 1886. 

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89. Lyon, T. L., and Fippin, E. O. The Principles of Soil Management. 4th 

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90. Ibid. P. 192. 

91. Mason, S. C. U. S. D. A., Bur. PI. Ind. Bui. 192. 1911. 

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WATER RELATIONS 99 

96. McMurran, S. M. U. S. D. A. Bui. 756. 1919. 

97. Mix, A. J. N. Y. Agr. Exp. Sta. Bui. 426. 1916. 

98. Morse, W. J. Me. Agr. Exp. Sta. Bui. 271. 1918. 

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104. Rixford, G. P. U. S. D. A. Bui. 732. 1918. 

105. Rosa, J. T. Jr. Proc. Am. Soc. Hort. Sci. 17: 207-210. 1920. 

106. Rotmistrov, V. G. Nature of Drought According to the Evidence of the 

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108. Schnee, F. Uber den Lebenszustand allseitig verkorkter Zellen. Dissertation. 

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109. Schwartz, F. Unters. a. d. Bot. Inst, zu Tubingen. 1: 140. 1883. 

110. Shear, C. L. U. S. D. A., Farmers' Bui. 1081. 1920. 

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112. Sorauer, P. Pflanzenkrankeiten. 3te Auflage. 1:169-170. Berlin, 1909. 

113. Ibid. P. 210. 

114. Ibid. P. 275, 284-285. 

115. Ibid. P. 286. 

116. Ibid. P. 324. 

117. Ibid. P. 332. 

118. Ibid. P. 335. 

119. Ibid. P. 422. 

120. Ibid. P. 435. 

121. Spoehr, H. A. Carnegie Inst. Wash. Publ. 287. 1919 

122. Stewart, J. P. Pa. Agr. Exp. Sta. Bui. 134. 1915. 

123. Stewart, J. P. Pa. Agr. Exp. Sta. Bui. 141. 1916. 

124. Taylor, E. P., and Downing, G. J. Ida. Agr. Exp. Sta. Bui. 99. 1917. 

125. Thompson, R. C. Ark. Agr. Exp. Sta. Bui. 123. 1916. 

126. Tucker, M., and von Seelhorst, C. .Journ. f. Landw. 46: 52-63. 1898. 

127. Tufts, W. P. Letter to one of the authors, dated March 21, 1921. 

128. U. S. D. A., Div. Agr. Soils Buls. 1, 2 and 3. 1895. 

129. Van Slyke, L. L., Taylor, O. M., and Andrews, W. H. Geneva Agr. Exp. Sta. 

Bui. 265. 1905. 

130. Von Seelhorst, C. Journ. f. Landw. 58: 83-88. 1910. 

131. Weaver, J. E. Cam. Inst. Wash. Publ. 286. 1919. 

132. White, J. Proc. Roy. Soc. Victoria. 24 (N. S.): 2-16. 1911. 

133. Whitehouse, W. E. Ore. Agr. Exp. Sta. Bui. 134. 1916. 

134. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 49. 1900. 

135. Whitten, J. C. Mo. Agr. Exp. Sta. Research Bui. 33. 1919. 

136. Widtsoe, J. A. Dry Farming. P. 185. New York, 1911. 

137. Wiggins, P. G. Am. Jour. Bot. 8: 30-40. 1921. 

138. Woodbury, C. G., Noyes, H. A., and Oskamp, J. Purdue Univ. Agr. Exp. 

Sta. Bui. 205. 1917. 

139. Zon, R. Proc. Soc. Amer. Foresters. 2: 79. 1907. 



SECTION II 
NUTRITION 

Nutrient supply is generally considered the most important of the 
factors limiting growth and productiveness. Certainly it ranks second 
to no other in determining the success or failure of the orchard enter- 
prise within those sections or areas where climatic conditions make 
possible a fruit industry and where economic conditions make practicable 
its development. Though there are many single cases in which the 
water supply, the prevalence of pests or some other factor assumes 
paramount importance, the most common limiting influence is associated 
with nutritive conditions. Much of the effort of the careful grower is 
directed toward relieving his plants from unnecessary competition and 
struggle for a nutrient supply. 

Few general questions pertaining to fruit growing have been less 
thoroughly understood than soil productivity as it relates to tree growth. 
This condition has existed mainly because of the assumption by analogy 
that the requirements of trees, vines or other fruit producing plants are 
practically identical with those of annual crops and because until very 
recently experimental evidence upon which to base reliable interpre- 
tations and conclusions has been lacking. Trees, shrubs and vines have 
life histories, even seasonal life histories, quite different from those of 
annuals. It is to be expected, therefore, that they possess quite different 
nutrient requirements or at least, quite different feeding habits. These 
nutrient requirements and feeding habits must be studied thoroughly 
before there can be a proper appreciation of the orchard soil productivity 
problem. 



100 



CHAPTER VII 

PLANT NUTRIENTS AND THEIR ABSORPTION 

Plants require for their nutriment water, carbon dioxide, oxygen, 
nitrates (or other nitrogen carrying compounds), sulphates, phosphates, 
salts of iron, magnesium, potassium and calcium. Though chemical 
analysis of plant tissue shows that almost every element may be found 
in one plant or another, carbon, hydrogen, oxygen, nitrogen, phosphorus, 
sulphur, potassium, magnesium, iron, calcium, chlorine, silicon, sodium, 
aluminum and manganese are found in practically all plants. The 
first ten of these are necessary for all the higher plants. Water, nitrogen 
and all the mineral elements are absorbed by the roots from the soil. 
Absorption by the leaves also occurs under certain circumstances but 
ordinarily this process may be disregarded. The water relations of 
plants have been treated in the previous section; the other plant nutrients 
absorbed from the soil form the subject of this chapter. 



DISTRIBUTION OF ELEMENTS FOUND IN ASH 

The mineral constituents of plants, except a part of the sulfur, are 
left as ash after the tissue has been burned. Some conception of the 
amount and composition of plant ash may be derived from the analyses 
of the wood, bark and leaves of the beech in Table 1. 

Table 1. — Ash Analyses of Wood, Bark and Leaves of Beech 144 





Ash K 2 


CaO 


MgO 


Fe 2 3 


P 2 6 


S0 3 


Si0 2 


Wood 


0.355 
5.860 
5.140 


14.4 

5.1 

21.8 


69.2 
83.4 
44.3 


4.5 
3.6 

7.2 


2.3 
0.7 
2.3 


2.7 
2.1 

7.8 


3.5 
1.0 
2.4 


10 


Bark 


3 7 


Leaves 


10.5 



In Tissues of Different Kinds. — The data in Table 2 on the amount 
and composition of the ash of apple trees, give an idea of the variations 
that may occur in the composition of different parts. The distribution 
of ash in the apple tree at the time of leaf fall is shown in Table 3. The 
ash percentage of bark is always many times that of the wood as Table 4 
shows. The ash content of seeds varies from 2 to 6 per cent. Thus, 
seeds of the chestnut contain 2.38 per cent, of ash, almonds 4.9 per cent, 
and coffee 3.19 per cent. 7 The composition of such ash appears from 
data presented in Table 5. 

101 



102 



FUNDAMENTALS OF FRUIT PRODUCTION 

Table 2. — Ash Analyses of Apple Varieties 140 



Ash in 
percent- 
ages of 
dry weight 



Si0 2 P 2 6 S0 3 CaO MgO Na 2 K 2 



(In percentages of ash) 



Branches : 

Haas 

Golden Sweet 
Hurlburt 

Trunks : 

Haas 

Golden Sweet 
Hurlburt 

Roots : 

Haas 

Golden Sweet 
Hurlburt 



3.93 
3.04 
4.92 

2.04 
2.29 
2.89 

5.64 
3.53 
4.34 



1.81 


7.35 


3.02 


43.68 


10.02 


2.51 


2.49 


5.89 


2.96 


40.60 


8.07 


7.09 


2.60 


4.44 


3.57 


41.55 


2.88 


4.98 


2.04 


2.13 


7.55 


44 . 52 


9.30 


1.33 


4.98 


4.61 


1.17 


41.96 


4.61 


3.91 


3.93 


4.08 


3.85 


44.80 


5.22 


2.48 


26.84 


9.44 


5.11 


32.98 


9.30 


4.74 


27.65 


7.71 


2.83 


26.99 


4.84 


3.87 


25.72 


4.17 


6.19 


25.20 


10.37 


7.22 



8.59 
3.37 
5.16 

6.96 
8.02 
1.31 

5.43 
2.00 

9.86 



Table 3. — Ash Analyses of a 7-year Old Apple Tree at the Time of Leaf-fall 23 
(In percentages of dry weight) 

Summer growth 3 . 57 

1-year old branches 2 . 83 

2-year old branches 2 . 76 

3-year old branches 2 . 75 

4-year old branches 1 . 87 

5-year old branches 1 . 78 

Trunk 1.33 

Large roots 1 • 83 

Small roots 4.51 



Table 4. — Ash Content of Wood and Bark 6 
(In percentages of dry weight) 




Wood 



Mahaleb cherry 
Sweet cherry . . . 
Horse chestnut . 



1.38 
0.23 

2.58 



Table 5. — Ash Analyses of Seeds 4 





K 2 


CaO 


MgO 


P 2 6 


SO, 


Chestnut 

Plum 1 


56.6 
26.5 


3.8 
8.4 


7.4 
16.1 


18.1 
34.8 


3.8 
7.1 







PLANT NUTRIENTS AND THEIR ABSORPTION 



103 



In Tissues of Different Age. — Age is likewise an important factor 
influencing ash content. The percentage of ash increases with age in 
the leaves and wood, but diminishes in the roots, branches and fruit. 
Though in these last it increases in absolute amount, the proportion falls 
off since organic matter increases at a greater rate. Table 6 shows the 
increase in ash content of beech wood with age. 

Table 6.— Ash Content of Beech Wood 209 
(In percentages of dry weight) 
Years of Rings 

1 to 15 1 . 162 

15 to 25 0.825 

25 to 35 . . . 645 

35 to 45 0.612 

45 to 60 . 555 

60 to 83 . 458 

83 to 94 (sap-wood) . 205 

At Different Seasons. — An increase in the percentage ash content 
of apple, pear, cherry and plum leaves during the season is shown in 
Table 7. The absolute amount of ash present declines, however, before 
the leaves fall (Table 8). Developing fruits, on the other hand, show a 

Table 7. — Ash Content op Leaves 155 (in percentages of dry weight) 



Apple 



Pear 



Cherry 



Plum 



May 9.. 
May 14. 
May 18. 
June 22. 
Aug. 29. 
Sept. 30 
Oct. 2.. 
Oct. 15. 



8.304 



8.017 
9.166 



10.889 



6.908 



7.157 
9.454 

9.552 



9.006 

10.510 
12.319 

14 . 446 



7.369 
15.031 
17.757 

20 . 987 



Table 8. — Grams of Ash in 100 Leaves 155 





Apple 


Pear 


Cherry 


Plum 




Ash 


Fresh 
weight 


Ash 


Fresh 
weight 


Ash 


Fresh 
weight 


Ash 


Fresh 
weight 


July 14 


2.876 
3.016 
3.576 
3.214 


95.15 
89.60 
95.10 
91.81 


1.270 
1.469 
1.548 
1.638 


47.19 
46.73 
42.98 
42.93 


2.494 
2.568 
2.814 
2.920 
3.214 
2.215 


76.48 
64.73 
65.83 
64.98 
74.61 
52.97 


3.038 
2.721 
2.693 

2.822 

3,076 


70 07 


July 31 


59 73 


Aug. 18, 21 


49 67 


Sept. 3, 4, 6 

Oct. 7 


50.20 


Oct. 23, 27, 29 






1.311 


36.22 


55 85 


Nov. 4 


2.541 


66.46 









104 



FUNDAMENTALS OF FRUIT PRODUCTION 



decrease in the percentage of ash and an increase in the absolute amount. 
The data in Table 9 illustrate these changes. The large increase in the 

Table 9. — Ash Content of Fruit 149 





Pear 






A.pple 




Date 


Percent- 
age of dry 
weight 


Absolute 

amount, 

grams 


Date 


Percent- 
age of dry 
weight 


Absolute 

amount, 

grams 


May 26 


7.96 
. 5.50 
4.32 
2.87 
3.27 
2.73 
2.27 
1.76 
1.46 
1.56 
0.91 
1.31 


0.0017 

0.0068 

0.0198 

0.0269 

0.043 

0.057 

0.069 

0.068 

0.079 

0.098 

0.065 

0.090 


June 2 


8.88 

5.09 . 

3.44 

2.89 

1.80 

1.33 

1.78 

1.43 

1.33 

1.07 

0.80 

1.67 

1.58 


0.0019 


June 5 


June 12 


. 0066 


June 15 


June 22 


0.011 


June 25 


July 2 

July 12 

July 22 

Aug. 1 

Aug. 11 

Aug. 21 

Aug. 31 

Sept. 10 

Sept. 20 

Sept. 30 


0.026 


July 5 

July 15 


0.034 
0.044 


July 25 

Aug. 4 

Aug. 14 

Aug. 24 

Sept. 3 

Sept. 8 


0.070 
0.075 
0.076 
0.079 
0.066 
0.160 




0.150 



ash content of the fruit affects the ash content of the spur on which the 
fruit is borne. Figure 10 shows a rapid decrease in the percentage ash 




Fig. 10. — Ash content of apple spurs in percentages of dry weight; bearing spurs 
represented by continuous lines marked W, B and J for Wealthy, Ben Davis and Jonathan 
respectively; non-bearing spurs shown by broken lines marked J and B\ barren spurs 
represented by dot-dash lines marked B and N for Ben Davis and Nixonite. (After 
Hooker. 100 ) 

content of bearing spurs beginning the latter part of May or in June 
and continuing until the fruit is picked. 100 In a summer apple like 
Wealthy, the curve rises in September, the fruit having been picked in 



PLANT NUTRIENTS AND THEIR ABSORPTION 105 

August. In Ben Davis and Jonathan, the fruit of which is picked the 
beginning of October, the curve does not rise until November. Spurs 
in the off year and barren spurs have no such characteristic decrease 
in ash content during June. 

ABSORPTION 

Mineral constituents and nitrogen are absorbed by the plant mostly 
through the roots. They are present in the soil as salts in solution and 
are taken up in large part by osmosis along with the soil water, the 
osmotic system being the same as that involved in water absorption. 

The Osmotic System. — The soil solution and the cell sap are sepa- 
rated by a semi-permeable membrane, through which the salts present in 
the soil solution are able to enter though the organic substances within the 
cell are, for the most part, incapable of passing in the opposite direction. 
Inorganic salts dissociate to a considerable degree, so that in a solution of 
sodium chloride, for example, there are present, besides molecules of 
salt, ions of sodium and ions of chlorine. These separate ions have the 
same value in regard to osmotic concentration as entire molecules; 
consequently a solution of inorganic salts is capable of producing a higher 
osmotic pressure than a solution of organic compounds having the same 
number of molecules in a given volume. In order that absorption of the 
various mineral constituents should take place by osmosis, the concentra- 
tion of each salt within the plant must be less than its concentration in 
the soil solution. Though, as previous analyses have shown, plant 
tissue contains considerable amounts of these mineral elements the plant 
is still able to absorb material from an exceedingly dilute soil solution 
which, in many cases, contains a lower percentage of a given constituent 
than the plant tissue itself. This is possible because the constituents in 
the plant are insoluble or are combined in an organic form. Since in 
either case they are removed from the osmotic system, the effective con- 
centration of inorganic salts within the plant remains less than that of 
the soil solution. It is evident, though, that a certain concentration of 
salts in the soil is necessary for osmotic absorption. In other words, the 
plant is unable to avail itself of all the mineral matter of the soil solution. 
However, very dilute solutions are often sufficient for ordinary growth. 

Thus "Birner and Lucanus many years ago found that mature crops of good 
yield could be grown in a well water containing about 18 parts potassium (K) 
and about 2 parts phosphoric acid (PO4) per million of solution and very satis- 
factory growth of wheat has been obtained in the water from the Potomac 
River, which contained about 7 parts per million of potassium." 24 

When these facts are combined with the conclusions reached by 
Cameron and Bell, 24 that the concentration of the soil solution, with 
respect to the principal mineral plant nutrients, is sufficient for the growth 



106 FUNDAMENTALS OF FRUIT PRODUCTION 

and development of crops and that the magnitude of the concentration 
is the same for practically all soils, one might easily be led to the belief 
that fruit plants seldom suffer from lack of an adequate supply of mineral 
nutrients. However, this inference is hardly warranted for, as is shown 
later, mineral nutrients may be in solution and still be unavailable to the 
plant. In other words solubility and availability are not synonymous. 
Furthermore, it may be noted that the 5 parts of water soluble nitrates 
per million of dry soil found by Gourley and Shunk 81 in sod-mulched orch- 
ards during the growing season were apparently insufficient for satisfactory 
wood growth and fruit production, while a concentration of 15 to 40 parts 
per million under certain other systems of culture proved entirely ade- 
quate. In this case all the nitrogen measured was in an available form. 
Whether in the sodded area nitrogen could be absorbed by the trees only 
when the concentration in the soil reached a certain minimum, or whether 
a very limited amount was absorbed even at the lowest concentrations, 
cannot be stated from available data; they show clearly, however, that 
the trees were unable to remove nitrates completely from the soil and 
further, that a nutrient solution very dilute in respect to this element 
provides only for very slow growth. 

Displacement. — The amounts of the various inorganic constituents 
in the soil are subject to variation and exchanges of bases may occur when 
they are present as silicates. Potassium, ammonium, magnesium, 
sodium and calcium form a series in which each member is capable of 
displacing any member following it in the series. One of two things 
may happen: an essential element may be lost to the plant by becoming 
soluble and being washed out of the soil, or it may be changed from an 
unavailable to an available compound and so placed at the disposal of 
the plant. 

Of most common occurrence is the displacement of calcium by 
potassium or sodium, resulting in the calcium salts going into solution. 
However, large amounts of calcium are capable of displacing small 
amounts of potassium 174 or any other base standing ahead of it in the 
series. Hence, calcareous soils are likely to be deficient in potash 
and the application of calcium in great amounts tends to deplete the 
potassium supply. Grape-fruit seedlings have been observed to show 
injuries characterized by yellowing of the foliage due apparently to 
the presence of ground limestone; more injury was evident in sandy 
soils than in loams. 66 One type of this yellowing is "frenching," a 
lack of green color in the areas between the largest veins, which is shown 
later to be a characteristic symptom of potassium starvation. ' 'Trench- 
ing" was produced also by sulphate of ammonia or organic fertilizers 
containing ammonia. This effect may be attributed to displacement 
of potassium in the soil by relatively large amounts of ammonia. 

The effects on the plant of displacement of bases may be indirect 



PLANT NUTRIENTS AND THEIR ABSORPTION 107 

rather than direct, for the displacement elements may combine to form 
more soluble salts and thus be rendered more available. 

As an instance, according to Loew: 124 "Lime and gypsum can also in cer- 
tain cases release such potash in the soil as is still unavailable. This, as well as 
the enhanced root-hair production under the influence of the increased amount 
of lime, accounts for the greater absorption of potash by the plant on soils rich 
in lime." 

Displacement would of course be of little value to the plant if the 
elements released were washed from the soil as a result of the greater 
solubility of their salts. 

Availability of Ash Constituents. — The soil constituents are of use 
to the plant only when combined in certain specific chemical compounds. 
Thus, sulphur must be present as sulphate, phosphorus as phosphate, and 
the various bases as relatively soluble salts. 

Availability and Solubility Distinguished. — Solubility, however, is 
only the first prerequisite to availability and absorption; it is not an 
absolute criterion of the crop-producing power of soils, as is indicated by 
studies on many soils in this country 24 and by investigations on the red 
soils of the "djati" forests of Java. 11 Nevertheless, "in general it can 
be said that a very heavily fertilized or extremely rich soil gives a greater 
solubility product than an unfertilized or poor soil." 16 Conversely 
"as a result of laboratory studies it appears that the constituents of 
soils which have been cropped for a long period of years go into solution 
at a somewhat slower rate than do those of the corresponding virgin 
soils." 130 

Factors Influencing Solubility. — The solubility of soil ingredients is 
affected by such factors as temperature, moisture content, chemical 
composition of the soil and root activity. According to McCool and 
Millar 130 the rate of solution is more rapid at 25°C. than at 0°C. The 
concentration of the soil solution apparently depends also on the 
relative masses of the soil and water. 

"At the ratio of 1 of soil to 5 of water the rate of solubility of natural soils 
is also slow and the extent of solubility extremely small. In fact, the amount of 
material that went into solution at this water content is only about half as much 
as that at the water content of 1 of soil to .7 of water, and yet an apparent 
equilibrium was attained. . . . The amount of material that goes into solution 
seems to increase as the ratio of soil to water is increased up to about the opti- 
mum moisture content and then it decreases." 16 

The effect of chemical composition on solubility is discussed by 
Bouyoucos. 16 

"As a whole it appears that the phosphates tend to depress solubility and that 
they probably act as conservers of bases under field conditions." Other salts, 



108 



FUNDAMENTALS OF FRUIT PRODUCTION 



however, tend to increase solubility. "The result of solubility of these singly 
salt treated soils goes to indicate that a salt or fertilizer treatment leaves a resid- 
ual effect upon the soil and this residual effect continues to be manifested in in- 
creased solubility and in increased crop-producing power." 

Availability of Phosphorus. — It has been stated that phosphorus 
is available to the plant only when present as a phosphate and that sul- 
phur is absorbed only as sulphate. However, all phosphates and sulphates 
are not equally available; furthermore, a phosphate that is highly avail- 
able for the plants of one species may be much less available to those of 
another. This principle is well illustrated by the data presented in 
Table 10 showing the percentage of normal growth made by plants grown 
in nutrient solutions that were uniform except for the form in which 
phosphorus was presented. 

Table 10. — Comparative Growth op Various Plants with Different 

Phosphates 
(After Truog 18 *) 
(Growth on acid phosphate represented by 100) 









Kind 


of phosphate 








Kind of 
plant 


















Blank 


Alumi- 
num 


Tri- 
calcium 


Ferric 


Ferrous 


Rock 


Mag- 
nesium 


Man- 
ganese 


Oats 


6.8 


96.4 


70.5 


79.9 


82.9 


9.1 






Buckwheat. . 


3.6 


88.0 


70.1 


32.5 


63.3 


70.0 






Rape 


0.8 


96.4 


76.2 


23.4 


61.5 


46.8 






Corn 


8.6 


56.3 


26.8 


40.3 


19.3 


10.0 


21.3 


76.4 


Barley 


16.7 


104.7 


62.2 


133.5 


79.7 


25.8 


15.5 


125.3 


Alfalfa 


1.5 


78.6 


99.2 


93.6 


28.1 


38.3 


7.1 


20.8 


Clover 


1.0 


84.2 


64.5 


68.9 


23.6 


6.1 


26.7 


4.2 


Millet 


0.7 


86.7 


34.8 


103.8 


31.0 


4.1 


16.0 


73.8 


Serradella. . . 


0.6 


78.7 


90.4 


111.7 


28.2 


3.2 


49.9 


51.7 



In commenting on these data Truog 188 remarks: "The great differences 
exhibited by the various plants in their growths on the different phosphates 
indicate that plant characteristics play an important role in this connection. 
The fact that rape made a better growth on rock phosphate than on ferric 
phosphate, while in the case of oats the opposite was true, indicates that solu- 
bility alone is not the only factor involved in the utilization of these phosphates 
by plants. The remarkably vigorous growth of the barley with ferric phos- 
phate is another indication that aside from solubility or availability, some 
phosphates seem to serve the needs of certain plants better than others. The 
remarkable adaptability of certain soils to certain crops may partly be due to 
causes of this nature." 

Availability Varies According to Kind of Plant. — In general the avail- 
ability of inorganic soil constituents is increased by the activity of the 



PLANT NUTRIENTS AND THEIR ABSORPTION 109 

roots. Their solvent action is yet to be accounted for satisfactorily. 
Crocker suggests that the strong, insoluble pectic acids found in the 
walls of root hairs may be responsible for the absorption of bases and 
the setting free of mineral acids, which would have a localized and 
temporary solvent action on the soil. Various plants show great differ- 
ences in the dissolving power of their roots, or at least in their ability to 
obtain required nutrients. 

Hartwell 87 found that carrots secured all the phosphorus they required from 
a soil in which rutabagas and cabbage were practically unable to grow, while 
wheat, oats, white beans and soy beans ranged between these extremes. Simi- 
larly, he found "an ability of the soy bean to obtain from the deficient [in avail- 
able potassium] plots about two-thirds of their maximum requirements, whereas 
carrots obtained about half their needs, mangels about one-fourth and summer 
squash only about one-tenth." 

It is not clear to what extent this characteristic feeding power of 
various plants may be due to varying ability to dissolve the materials 
they encounter in a solid or colloidal form, what part may be due to 
varying ability to use nutrients combined in different forms (e.g., potas- 
sium in the form of a chloride instead of sulphate), or what part may be 
due to varying ability to absorb from very dilute solutions. This 
question needs careful investigation, particularly in its application to 
orchard and vineyard fruits of different kinds and to the stocks upon 
which they may be grown. It is conceivable that the high feeding power 
of a certain stock in respect to some particular material may be of as 
great significance in the success of a fruit plantation in a certain soil 
as the question of "congeniality" of stock and cion. From the data 
presented by Hartwell, the inference may be drawn that the potassium 
found in the soil and practically unavailable to mangels and summer 
squash would be made available to them were soy beans first grown 
upon the land and then plowed under, for, after the soy beans had 
dissolved and used it, other plants would find it in a different form. 
There may be little occasion for special efforts to make potash more 
available to orchard trees by using intercultures, for evidence is presented 
later that for fruit trees potash is seldom a limiting factor. Nevertheless, 
the general principle involved may be important in relation to other 
elements. 

Availability of Iron and Sulphur. — Certain types of bacteria oxidize sulphur or 
hydrogen sulphide to sulphates and others, ferrous oxide to ferric oxide. These 
organisms may play some part in rendering sulphur and iron available, though 
the most important type of bacterial action in the soil is concerned with general 
decomposition and particularly with the nitrogen supply. 

Availability of Nitrogen. — Just as sulphur is available only in the form 
of sulphate and phosphorus in the form of phosphate, most nitrogen is 



110 FUNDAMENTALS OF FRUIT PRODUCTION 

absorbed in the form of nitrate. However, nitrites and salts of ammonia 
can be utilized to a limited extent, different plants showing considerable 
variations in this respect. Organic nitrogen also may be a substitute for 
nitrate, though inorganic nitrogen compounds are used in preference. 
It has been shown that such nitrogenous soil constituents as nucleic 
acid, hypoxanthine, xanthine, guanine, creatinine, creatine, histidine, 
arginine and choline serve as sources of nitrogen when nitrates are absent, 
but not to any great extent when large amounts of nitrate are pres- 
ent. 163 ' 169, Moreover, the absorption of nitrate by plants grown in 
culture is always reduced when creatine or creatinine is present, though 
the total nitrogen intake remains fairly constant. These organic nitrogen 
compounds have no effect on potash or phosphorus absorption. 

Bacteria are of great importance in making organic nitrogen com- 
pounds in the soil more available to the plant and incidentally in destroy- 
ing toxic substances. Putrefying bacteria, for example, convert the 
nitrogen of organic compounds to ammonia and nitrogen gas. 

Hart and Tottingham 86 have shown that "soluble phosphates increase 
enormously the number of soil organisms and the rate of ammonification and 
destruction of organic matter, while the sulphates activate but slightly in these 
directions. The processes mentioned are admitted to be of great importance 
to the plant's nutrition and environment, involving, as they must, not only a 
more rapid formation of readily soluble compounds of nitrogen and a possible 
destruction of harmful organic materials, but a greater saturation of the soil 
moisture with carbon dioxide, resulting in increased solution of mineral materials 
necessary for rapid growth." Work at the Utah Experiment Station 82 indicates 
that sulphates have a particularly stimulating effect on soil bacteria under certain 
conditions. 

Nitrification. — The ammonia produced by bacterial action is in its turn 
converted to nitrites and these nitrites to nitrates by nitrifying bacteria, 
each of these changes being carried out by distinct organisms. These 
organisms require, for the process of nitrification, good aeration, involving 
both oxygen and carbon dioxide, a certain water supply, the presence of 
calcium or magnesium compounds, a medium temperature and freedom 
from an excess of soluble organic compounds or from free ammonia. It 
is evident that conditions favoring the action of nitrifying organisms will 
tend to increase the supply of available nitrogen. 

Aided by Liming. — It has been found that applications of lime in many 
cases increase nitrification. Table 11 presents the results of one such 
experiment with orchard soils in New Hampshire. Obviously in this 
instance liming benefited the soil in at least this one direction and it is 
possible that at the same time it exerted no harmful influence. However, 
data are presented later to show that it may have a very harmful effect 
through rendering iron unavailable. Consequently a single fertilizer 
application may produce at the same time both beneficial and harmful 



PLANT NUTRIENTS AND THEIR ABSORPTION 

Table 11. — Nitrates in Limed and Unlimed Plots 81 
(In parts per million of dry soil) 



111 



Year 


Limed plot 


Unlimed plot 


Surface soil 


Subsoil 


Surface soil 


Subsoil 


1913 
1914 
1915 
1916 


82.33 
82.46 
29.98 
98.48 


19.60 
23.43 
13.78 
24.16 


57.46 
57.09 
24.26 
80.36 


6.16 
15.21 
17.24 
11.56 


Average 


73.31 


20.23 


54.79 


12.54 



effects. These may just about neutralize each other and leave the plants 
practically uninfluenced by the treatment, or the one influence may 
greatly outweigh the other. Caution should be exercised, however, in 
making applications of lime to the orchard. 

Influenced by Methods of Soil Management. — Moreover different 
methods of soil management, particularly as they effect aeration and soil 
temperature have a marked effect on nitrate production. 

Gourley and Shunk 81 found that "the ratio of nitrates between sod, tillage 
and tillage with cover crops is as 1 : 5.4 : 10.6 in the surface soil and in the sub- 
soil as 1 : 3.3 : 3.7. At no time during the experiment have we obtained a 
sample under sod that showed more than 14.78 parts nitrates per million and the 
average for the 4 years is 3.18 p. p.m. with an average of 17.40 p. p.m. and for 
tillage plus a leguminous cover crop it has shown as high as 132 p. p.m. and the 
average is 33.91 p. p.m. for the 4 years." 

The nitrate determinations showing the result of 4 years' experiments 
on orchard soils are summarized in Table 12. Whether the small 
amount of nitrate under sod is the result of reduced nitrate produc- 
tion or merely the residue from a greater nitrate consumption by the 
plants constituting the sod, the effect on the orchard trees is the same. 
Under sod there is but little available nitrate. In Indiana also, it was 
found that in a young orchard most nitrates are formed under the clean 
culture-cover crop system of soil management, and the straw mulch 
ranked next. 206 The heavier the mulch, the later in the spring does 
bacterial activity begin because of the lower temperature and the later 
in the fall does it persist as a result of the higher temperature of 
the soil. 

It is probably because of their influence upon nitrate formation that 
various tillage methods have so generally proved superior to sod manage- 
ment methods in promoting both vegetative growth and fruit production. 
This is true particularly in areas that are more humid or have deeper 
soils. On the other hand, in sections having a long dry period during 



112 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 12. — Water Soluble Nitrate in Parts per Million of Dry Soil 81 

(Average per plot) 



Year 



Sod 



Tillage 



Tillage with cover 
crop 



Surface soil 



1913 
1914 
1915 
1916 



Average . 




18.25 
14.01 
21.05 
16.29 

17.40 



38.37 
37.27 
18.75 
41.26 

33.91 



Subsoil 



1913 


1.55 


6.90 


6.87 


1914 


3.56 


6.62 


. 10.81 


1915 


1.51 


10.76 


6.88 


1916 


2.18 


5.05 


8.05 


Average 


2.20 


7 . 33 


8.15 



the summer, wherever the soils are of such nature that they encourage 
shallow rooting the influence of these various systems of soil management 
upon moisture supply is probably a factor of equal or greater importance. 
However, it is neither difficult nor expensive to furnish trees growing in 
sod with an adequate supply of nitrates through the use of certain fertil- 
izers. Indeed, it is in orchards of this kind that nitrogenous fertilizers 
have given some of the most striking results and the question may be 
raised whether some nitrogen-carrying fertilizer may not be a more or 
less constant requirement if orchards permanently under this method of 
soil management are to be kept growing and producing most efficiently. 

Influenced by Temperature and Soil Moisture. — The effects of moisture 
and of temperature on the activity of nitrifying bacteria are shown by a 
seasonal variation in nitrate content. For example, in Illinois soils 210 
the most active season of nitrate production and accumulation is late 
spring and early summer when optimum moisture and temperature 
conditions are approached. Early autumn is the next most active 
season, when these optimum conditions for nitrate production are fre- 
quently approached. During the summer little nitrate is produced 
unless the weather is cool and moisture plentiful; in winter there is no 
evidence of nitrate production. 

Similar conditions are reported for orchard soils in Indiana 206 where 
very little nitrate was found in late fall and winter, though maxima were 
found in early summer and early fall. Orcharding, however, is carried 



PLANT NUTRIENTS AND THEIR ABSORPTION 113 

on in many sections where seasonal and soil conditions are materially 
different from those of Illinois and Indiana and it is conceivable that 
under certain environmental conditions nitrate production, even under 
sod, might keep pace with the tree's requirements for nitrogen. 

Losses of Nitrogen from the Soil. — Nitrates are very soluble in 
water and unlike most of the mineral nutrients, are not adsorbed or 
otherwise fixed in the soil to any considerable degree. Heavy rains or 
heavy irrigation washes them out and carries them away in the drainage 
water. In one Florida experiment this loss from leaching was found to 
equal the nitrate content of over 800 pounds of nitrate of soda per acre 
during a 10-month period. 4 Not the least important function of cover 
crops is to take up the nitrates that are being formed in late summer and 
autumn, to store their nitrogen in organic form during the winter and to 
return it to the soil — thence to the trees — the following growing season, 
thus preventing a large loss through drainage. The advantage of a 
soil, and of orchard management methods, permitting deep rooting and the 
storage of large quantities of capillary water minimizing seepage losses, 
is evident. 

Maintaining the Nitrogen Supply of the Soil. — Despite the means 
that may be taken to prevent undue loss of soil nitrates, crop production 
alone removes considerable quantities and unless the supply of nitro- 
genous compounds from which they are derived is maintained the time 
will come when they cannot be formed in quantities sufficient for maxi- 
mum crop production. The organic matter of the. soil is the storehouse 
of these nitrogenous compounds and with its gradual depletion the 
nitrogen problem becomes acute. It is well known that constant tillage 
is one of the most effective means of reducing or "burning out" humus 
supply. Consequently the cultural methods in the orchard that make 
nitrogen available most rapidly, deplete the total supply most rapidly. 
Indeed it may be questioned if, over a long period, the orchard under a 
strictly clean-culture method of management will not need heavier 
nitrogen fertilization than the one in sod. 

Some measure of the cumulative effect of tillage as compared with a sod 
covering on total nitrogen supply is contained in the following statement: 
"Analysis of soil taken from this land at the time the experimental work was 
started indicated a nitrogen content of 5,000 pounds per acre. After this soil 
had been cropped and cultivated for 20 years, the nitrogen content was approxi- 
mately 4,000 pounds per acre. Adjacent soil which was in grass during the 20- 
year period contained 5,600 pounds of nitrogen." 4 It is significant that, though 
there was a loss of 20 per cent, of the total nitrogen supply of the soil during the 20 
years in the cultivated land, there was an actual increase of 12 per cent, in the 
sod land during the same period. This can be attributed to nitrogen fixation, 
particularly by leguminous plants in the sod, in addition to the nitric acid 
contributed by rain water. 

8 



114 FUNDAMENTALS OF FRUIT PRODUCTION 

The likelihood of trees under one of the two standard systems of 
orchard culture suffering from lack of available nitrogen and, on the other 
hand, the nearly absolute certainty that under the other system the 
soil will have its total nitrogen reserve seriously depleted, suggest 
that a combination of the two methods possibly might afford a means of 
maintaining permanently the nitrogen supply of the soil and at the same 
time obviate the necessity of supplying the trees artificially with readily 
available nitrates. Such a combination might consist in alternating 
sod and cultivation each in 2-year periods or, better still, in maintaining 
alternate tree rows, the "middles," under the two respective systems 
and then occasionally reversing the treatments on these alternate strips. 
The marked success that frequently has attended such a combination is 
evidence of its practicability under many conditions. Such a combina- 
tion treatment is a compromise also in its influence upon soil moisture 
supply and soil erosion. In some instances it might prove undesirable 
because of the increased difficulty in controlling certain orchard pests 
which are best held in check by cultivation. 

Few, if any, of the plant nutrients obtained from the soil are subject 
to such great variation from season to season and even from week to 
week as is nitrogen; likewise few are so completely under the control of 
the grower through methods of soil management. It is largely because of 
the first two facts that the problem of maintaining fertility in the orchard 
generally centers around the nitrogen supply. The discussion that has 
preceded serves also to bring out clearly the fact that proper treatment 
of the soil may reduce or altogether remove the necessity for nitrogen 
fertilization and that, on the other hand, there are instances where it may 
be true economy not to employ those practices that will lead to greatest 
nitrate formation but deliberately to limit this process and supply the 
deficiency by artificial means. 

Nitrogen Fixation. — Nitrogen gas is not available to the higher plants, 
but it is acted upon by nitrogen-fixing bacteria which convert it either 
to nitrates or to other nitrogenous compounds that in due time are con- 
verted into nitrates. Some of these bacteria are able, independent of any 
association with the roots of higher plants, to fix this atmospheric nitro- 
gen and thus effect the first step in rendering it available. 69 ' 70 Indeed 
there are conditions under which their activity is so great that the resul- 
tant accumulation of nitrates renders the soil toxic to trees and other 
plants. 93 For the most part, however, nitrogen fixation by bacteria 
is effected by forms living in colonies on the roots of leguminous plants 
where they produce nodules or tubercles. 

As very few of the species bearing edible fruits belong to the legume 
family, nitrogen-fixing bacteria are of comparatively little direct benefit 
except when they fix nitrogen in the absence of host plants. However, 
they become of great value indirectly when leguminous cover crops or 



PLANT NUTRIENTS AND THEIR ABSORPTION 115 

a sod including legumes is maintained. There are conditions under 
which it is difficult or impracticable to grow legumes in the orchard; 
nevertheless their special value should not be overlooked, particularly 
where there is need of increasing the available nitrate supply. Their 
judicious use in place of some of the other cover or mulching crops or 
in the place of some other system of orchard management often obviates 
the necessity of supplying the trees with nitrogen through mineral or 
animal fertilizers. 

An instance of the results that can be obtained by the use of leguminous plants 
as cover crops is described by Coville. 35 " The trees in one newly planted orchard 
of Grimes apples have been kept in a remarkable condition of growth by one 
initial application of manure in the year of their planting, succeeded by the 
following rotation: In May the ground is sowed to cowpeas. These are plowed 
under in September and followed immediately by the sowing of rye mixed with 
hairy vetch. In the following May the mixed crop is plowed under. The 
same 1-year rotation has been followed year after year. Under this treatment 
the soil, which has the appearance of almost pure sand, has become so fertile 
without the application of lime, commercial fertilizer or manure that an occa- 
sional crop of cowpeas has been cut for hay without serious interference with the 
progress of the orchard." The successful use of such a system would depend 
upon an abundant water supply. 

Were it possible to maintain permanently a good stand of clover, 
vetch, alfalfa or some other leguminous crop in the orchard and to leave 
the growth that it produced on the ground for a mulch, it would afford 
an almost ideal sod system of management — from the standpoint of 
maintaining soil fertility — though water competition between the trees 
and the intercrop would make it entirely impracticable under many 
circumstances. Under average conditions, however, the maintainance 
of such a sod is next to impossible because bluegrass or other species 
crowd out the legumes. Where such a legume sod can be maintained 
and the competition for moisture can be largely eliminated by irrigation, 
a system of soil management is possible that affords the trees excellent 
nutritive conditions for vigorous growth and heavy production and is 
at the same time economical. Various fungi found in the roots of certain 
heaths (Ericaceae), are likewise capable of fixing nitrogen. It is probable 
that the cranberry and blueberry obtain at least a portion of their nitro- 
gen supply through similar agencies. 

Soil Reaction : Acidity and Alkalinity. — The absorption of available 
inorganic salts by the root is affected to an important degree by acidity, 
concentration, toxicity, aeration and temperature of the soil and of the 
soil solution. The reaction of the soil solution is of great importance. 
Most plants thrive best when the soil is very weakly acid. Many water 
plants live better in a very weakly alkaline solution, while land plants 
show marked differences in the amount of acidity which they will endure. 



116 FUNDAMENTALS OF FRUIT PRODUCTION 

When the acidity of the soil increases beyond the low value which is 
most favorable to land plants, it becomes an important factor. 

Soil Reaction and the Availability of Phosphorus. — The effect of soil 
acidity on the availability of phosphorus is shown by the following 
quotation from Harris: 85 

"In addition to the work that has been done on determining the degree of 
soil acidity, many investigations have been undertaken to determine the relation 
of soil acidity to the quantity of available phosphorus in the soil. As a result 
of the work of Wheeler, Thorne, Whitson and Stoddart, it has been show that the 
content of this element is generally low in acid soils and largely unavailable for 
use by plants. Stoddart explains this by saying that acid soils convert any 
calcium phosphate that may be present into soluble compounds which are either 
washed out or are fixed in an insoluble form by the formation of iron and alumi- 
num phosphates." 

Soil Reaction and the Availability of Iron.- — An excess of calcium salts 
affects the availability of iron in such a way that many plants grown on 
calcareous soils suffer from lack of iron, even though iron is present in 
considerable amounts. It is from this cause that grape vines and fruit 
trees become chlorotic on some of the calcareous soils of France and 
England, pineapples and sugar cane on Porto Rican soils containing 
large amounts of lime and citrus fruits in Florida when ground limestone 
is added to the soil. 

"In Porto Rico the extension of the pineapple industry has been retarded 
by a disease known as chlorosis, the principal external mark of which is the 
yellowing of the foliage and the consequent poor nutrition of the plant. From 
investigations by Gile and by Loew it appears that the yellow color of the leaves 
and the accompanying weakness of the plant are due to the lack of iron, and that 
where the soil contains an excess of lime the organic acids which are needed to 
dissolve the iron of the soil are themselves neutralized and the iron, although 
present, is not available for absorption by the pineapple roots." 35 

According to Gile and Carrero, 72 sugar cane grown on the calcareous soils 
of Porto Rico suffers from chlorosis. Analysis shows that the ash of these chlor- 
otic leaves has less iron then normal leaves. 

Floyd 66 describes two types of injury to grape-fruit seedlings from the presence 
of ground limestone in the soil. In addition to frenching which has been dis- 
cussed, chlorosis occurs. This type of injury may be attributed to iron deficiency 
and is probably quite distinct from frenching, since no case of the latter was 
observed to develop into complete chlorosis. The larger the amount of limestone 
in the soil the greater was the injury observed. 

The unavailability of iron in calcareous soils is probably attributable 
to the alkaline reaction produced by an excess of calcium salts in solution. 
Colloidal iron hydroxide is formed in alkaline solutions and is for the 
most part unavailable to plants. Similar conditions prevailing in man- 
ganiferous soils confirm the idea that the basic reaction of the soil solu- 



PLANT NUTRIENTS AND THEIR ABSORPTION 117 

tion, rather than the presence of specific calcium or manganese compounds, 
is responsible for the formation of iron hydroxide. 

Pineapples grown in Hawaii on the black manganese soils of the island of 
Oahu suffer from chlorosis. This condition is recognized by yellowing of the 
leaves, stunted red or pink fruits, many of which crack open and decay and 
other toxic effects. 198 Other crops grown on these manganese soils suffer 
similarly, especially corn, pigeon peas, cowpeas and rice. On the other hand, 
sugar cane is less sensitive and certain weeds such as the sow thistle, Waltheria 
americana and Crotalaria sp., show no effects from manganese. 106 The difference 
between these two types of plants was revealed by ash analyses. Those to 
which the soil is toxic have less iron in their ash when grown on manganiferous 
soils than when grown on ordinary soils. The ash of the weeds growing wild on 
the manganese soils without apparent ill effects showed no decrease in iron, con- 
taining even more than when grown on other soils. 198 

The other elements in the ash showed no such significant variation, though 
in practically every instance the absorption of manganese was increased on the 
manganese soil and with it the absorption of calcium. 

The unhealthy growth on the manganese soil thus appears to be due 
to a lack of available iron. The plants suffered from iron starvation in 
spite of the 10 to 30 per cent, of iron oxide in the manganese soils. 

Applications of iron sulphate to the soil, at rates varying from 500 to 
3000 pounds to the acre, were unsuccessful in preventing chlorosis; 
but less than 50 pounds of iron sulphate per acre sprayed on the leaves 
effected a prompt cure. 91 This is of particular interest for it shows that 
pineapple leaves can absorb enough iron to cure chlorosis, though the 
roots are not able to do so under the circumstances. It has been found 
that the chlorosis of many coniferous seedlings growing on a calcareous 
soil can be remedied by spraying with a 1 per cent, solution of iron sulphate 
and this treatment has become a regular practice in certain nurseries. 112 
An interesting treatment more or less generally and successfully used 
in France and Germany for the cure of chlorosis in grape vines 152 
consists in brushing the cut surfaces of pruned vines with a concentrated 
solution of ferrous sulphate. Filling, with a soluble iron salt, holes bored 
in chlorotic trees frequently has been tried in New Mexico and generally 
with satisfactory results. 139 

From this discussion of the effects of calcium and manganese on 
iron, it is evident that fertilization may be of value, not only for adding 
plant nutrients to the soil, but also under certain conditions, for rendering 
soluble and available to the plant, nutrients that though present are 
unavailable. Conversely, ill advised fertilization may change mineral 
elements that are present from a soluble to an insoluble form and there- 
fore make them unavailable to the plant. Through this effect liming has 
led to chlorosis of the pineapple in Porto Rico. 73 It would be of interest 
to know the results following direct attempts to change the reaction of the 



118 FUNDAMENTALS OF FRUIT PRODUCTION 

solution of calcareous or manganiferous soils where chlorosis is produced. 
Possibly the application of acid in some form would be as effective in 
preventing chlorosis as the application of iron salts to the leaves or cut 
surfaces. 

Acid Tolerance of Certain Crops. — Most deciduous orchard fruits are 
acid tolerant to a considerable degree. The strawberry has been shown 
to prefer an acid soil 207 and the blueberry 34 demands a soil markedly 
acid in reaction. In the practically neutral reaction of a good garden 
loam it fails to thrive or even dies out. The superior development 
of wild raspberries, blackberries, dewberries and haws in soils that are 
at least slightly acid suggests that their cultivated relatives may be 
at home in similar soil conditions. That deciduous fruits are not alone 
in their tolerance or preference for soil acidity is indicated by the behavior 
of citrus trees in acid soils. 

Collison 31 in reporting the results of a series of fertilizer experiments in Florida 
says: "So far as could be noted an acid soil has no injurious effect on the growth 
of the orange tree. On some of the most acid plots in the grove the trees are 
vigorous and have made very good growth, ranking well up among the best plots 
in the grove." 

Furthermore, practically all of the best orchard cover crops are dis- 
tinctly acid tolerant. The following commonly used cover crops belong 
in this class; cowpeas, soy beans, hairy vetch, crimson clover, rye, oats, 
millet, buckwheat and turnip. 35 

Since deciduous fruit plants are predominantly acid tolerant, they 
should not be exposed to a markedly alkaline reaction of the soil. Ammo- 
nia in considerable amount depresses root growth and eventually kills 
the roots, because of its effect on the soil reaction. Injuries resulting 
from an excess of "alkali," as the term is generally used in the arid and 
semiarid sect ons, are due not to any effect these salts may have on 
the reaction of the soil, but rather to the excessive concentration of 
the potassium and sodium salts that are present. The difference between 
the toxic symptoms attending an alkaline or basic soil reaction and those 
attending impregnation with "alkali" is well marked. A soil solution 
having an alkaline reaction affects the roots before the shoots; the toxic 
effects of a soil solution which is too concentrated are evident first in the 
shoots. 

Concentration: Soil "Alkali." — As just pointed out, the term "soil 
alkali" does not refer to the soil reaction, but to an excessive concentra- 
tion of certain salts. The carbonates, chlorides and sulfates of sodium 
and potassium are concerned chiefly, though occasionally other salts 
accumulate in such amounts as to be injurious. 

Tolerance of Different Fruits. — The degree of tolerance of various fruit 
crops to salts of different kinds is indicated by data presented in Table 13. 



PLANT NUTRIENTS AND THEIR ABSORPTION 



119 



Table 13. — Highest Amount of Alkali in Which Fruit Trees Were Found 

Unaffected 

(After Loughridge 12b ) 

(Pounds per acre in 4 feet depth) 



Sulphates 


Carbonates 


Chlon 


d 


Total 


alkali 


(Glauber salt) 


(Sal soda) 


(Common 


salt) 


Grapes. . 


. 40,800 


Grapes . . . 


.. 7,550 


Grapes 


9,640 


Grapes. . 


. 45,760 


Olives. . 


. 30,640 


Oranges. . 


. . 3,840 


Olives 


6,640 


Olives . . . 


. 40,160 


Figs... . 


. 24,480 


Olives .... 


.. 2,880 


Oranges 


3,360 


Almonds. 


. 26,400 


Almonds 


. 22,720 


Pears .... 


.. 1,760 


Almonds. . . . 


2,400 


Figs 


. 26,400 


Oranges. 


. 18,600 


Almonds. . 


.. 1,440 


Mulberry . . . 


2,240 


Oranges . 


. 21,740 


Pears . . . 


. 17,800 


Prunes. . . 


.. 1,360 


Pears 


1,360 




. 20,920 


Apples . . 


. 14,240 


Figs 


. . 1 , 120 


Apples 


1,240 


Apples. . . 


. 16,120 


Peaches. 


. 9,600 


Peaches. . 


.. 680 


Prunes 


1,200 


Prunes . . . 


. 11,800 


Prunes. . 


. 9 , 240 


Apples.. . . 


640 


Peaches 


1,000 


Peaches. . 


. 11,280 


Apricots 


. 8,640 


Apricots . . 


480 


Apricots. . . . 


960 


Apricots. 


. 10,080 


Lemons . 


. 4,480 


Lemons. . . 


480 


Lemons 


800 


Lemons. . 


. 5,750 


Mulberrj 


'. 3,360 


Mulberry . 


160 


Figs 


800 


Mulberry 


. 5,740 



Loughridge 125 makes the following comments on these data: "The amount 
tolerated depends largely upon the distribution of the several salts in the vertical 
soil column, the injury being most severe in the surface foot, where under the 
influence of the unfortunate practice of surface irrigation the feeding rootlets 
are usually found. It is therefore important that in alkali regions such methods 
of culture and irrigation should be followed as to encourage deep rooting on the 
part of crops. 

"The amount tolerated varies with the variety of the same plant, as shown 
in the grape." For instance, Flame Tokay is reported as "not growing" with a 
total of 24,320 pounds of alkali in the surface 4 feet per acre while Trousseau is 
reported as thrifty in the presence of 31,360 pounds, though the sal soda content 
of the Flame Tokay soil was somewhat higher but still well within the general 
tolerance limit of the grape for this salt. 

"The amount of alkali tolerated by the various cultures varies with the 
nature of the soil. It is lowest in heavy clay soils and fine-grained soils, in 
which the downward movement of plant roots is restricted; and highest in loam 
and sandy soils, in which the roots have freedom of penetration." 

Injuries from Excessive Fertilization.- — It is evident that continued 
application of fertilizer such as sodium nitrate may produce concentra- 
tions that are harmful. 

In discussing experiments with citrus trees Kelly and Thomas 107 state: 
"While the growth of the trees was notably stimulated by sodium nitrate during 
the first few years of the experiment, and healthy, normal appearing trees were 
produced, since that time excessive mottle leaf has appeared on every tree in 
this plot. The mottling here became so severe during the past 2 or 3 years as 
to render the trees wholly unprofitable. No marketable fruit whatever is now 
produced by these trees." 



120 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 14 presents data showing the toxic limits of citrus seedlings 
for various nitrate salts and for ammonium sulphate and the toxic limits 
for these salts in the presence of lime. Their lesson in connection with 
the use of commerical fertilizers in the orchard is well summarized in the 
words of Breazeale: 18 

"It will be seen that marked differences occur in the toxic limits of the various 
salts, sodium nitrate being five times as toxic as calcium nitrate. The toxic 
limits for this group of salts are so high that the matter may appear to be of no 
practical import. But a simple calculation will show that the surface feeding 
roots of citrus trees are at times subjected to fertilizer concentrations in field 
practice so great as to approach toxic conditions. Application of 2 to 3 pounds of 
nitrate of soda per tree, or 200 to 300 pounds per acre, which is not an unusual 
practice for some citrus growers, would correspond approximately to a concen- 
tration of 70 to 100 parts per million in the soil of the surface foot. The fertilizer, 
moreover, is ordinarily applied to the open ground between the tree rows — that is 
not more than one-half the total soil area. If the moisture content of the soil 
were reduced to 10 per cent, of the weight of the soil, the concentration of the 
sodium nitrate in the soil solution would range from 1,400 to 2,000 parts per 
million — that is, it would approach the toxic limit. The surface crusts in citrus 
groves are often highly toxic to citrus seedlings." 

Table 14. — Toxic Limits of Nitrates and Ammonium Sulphate for Citrus 

Seedlings 18 

Toxic Limit 
Salt Parts per Million 

Sodium nitrate 1 , 800 

Potassium nitrate 3 , 500 

Calcium nitrate 10 , 000 

Ammonium sulphate 1 , 000 

Sodium nitrate and calcium carbonate (solid phase) 6,000 

Ammonium sulphate and calcium carbonate (solid phase) 2,000 

Some Effects of Soil Alkali. — The effects of excessive concentration 
produced by "alkali" on citrus trees are described by Kelly and 
Thomas. 107 

"Different varieties and species of citrus trees are affected differently by 
alkali. Lemon trees show the effects by a pronounced yellowing of the margins 
and burning of the tips of the leaves, followed by unusually heavy shedding of the 
leaves in the latter part of the winter and spring. The subsequent new growth 
may appear to be quite normal and vigorous for several months, but later a large 
portion of the leaves turn yellow in irregularly shaped areas around the margins 
and fall excessively. In the presence of excessive concentrations of salts, espe- 
cially chlorides, complete defoliation may take place. Mottle leaf frequently 
occurs, and sometimes chlorosis. Both the quality and quantity of the fruit are 
impaired. 

"It has been found that orange trees affected by alkali are unusually sus- 
ceptible to injury from adverse climatic conditions. Hot winds burn the young 
leaves and frosts produce more serious injury than with normal trees. Alkali 



PLANT NUTRIENTS AND THEIR ABSORPTION 121 

injury is also accentuated by the lack of care, such as improper tillage, the insuffi- 
cient use of manure or other fertilizers, and withholding irrigation, thereby allow- 
ing the soil to become too dry. If the soil be allowed to dry out excessively, the 
concentration of alkali in the soil moisture may become harmful, while a more 
abundant supply of water would so dilute the salts present as to reduce the 
concentration to a point where normal growth could take place. 

" In certain localities the dissolved salts are predominantly chlorides, in others 
sulphates and in still others bicarbonates. A few wells have been found to contain 
large amounts of nitrates." 

Alkali in the soil may also have a marked effect on root distribution. 

"It is especially interesting that the roots of the lemon trees have not pene- 
trated deeply in this soil, more than 95 per cent, of them being within 18 inches 
of the surface. There is probably some connection between this fact and the 
higher concentration of alkali salts found in the third and fourth feet. 

"Local areas occur in a Valencia orange grove near Garden Grove in Orange 
County where many of the trees have been severely injured by alkali brought up 
as a result of a temporarily high water table in the winter and spring of 1916. 
The water table receded within a few months but the alkali salts remained in the 
soil. A considerable number of trees have recently died, and all of them in cer- 
tain areas became excessively chlorotic, following the rise of the alkali." 

When irrigation is practiced, the composition of the irrigation water is an 
important factor. Kelly and Thomas found from their investigations, "a 
remarkably close relationship between the composition of the irrigation water, 
on the one hand, and the accumulation of alkali salts and the condition of the 
orange and the lemon trees, on the other. In every case we have studied, where 
saline irrigation water has been applied for a series of years, alkaline salts have 
accumulated in the soil and the citrus trees have been injured in consequence. 
The rates at which salts have actually accumulated vary, however, in different 
soils, depending on (1) the composition of the water, (2) the amounts applied, 
and (3) the freedom with which it penetrated into the subsoil." 107 

The injurious effects of high concentrations produced by excessive 
amounts of alkali or other salts in the soil are due largely to the inability 
of plants to absorb water by osmosis from a solution having a higher 
osmotic concentration than that of the plant itself. Hence, the harmful 
effects of alkali are partly those of starvation and drought. The con- 
centration of the soil solution requires attention only under conditions 
where the salt content of the soil is naturally high, as in salt marshes and 
in regions near salt water generally, or where the moisture supply is 
restricted, as in arid or semiarid regions. However summer drought 
may produce temporarily excessive concentrations in any soil and so 
bring about injury. 

Remedial Measures. — When a soil once becomes impregnated with 
alkali about the only effective treatment is flooding the land with irriga- 
tion water to dissolve out the excessive amounts which are then either 
forced down to a depth where they will do no harm or carried away in 
the drainage water. Provision for thorough drainage is very important 



122 FUNDAMENTALS OF FRUIT PRODUCTION 

in places where there is danger from alkali, as the rise of the water table 
attending poor drainage may result in bringing salts from lower soil 
to the surface and thereby increase concentrations in the upper layers 
as evaporation takes place. Moderate, as opposed to excessive, irrigation 
is a preventive measure. Though there is not often a choice between 
two or more sources of irrigation water, the irrigation fruit grower should 
remember that certain water supplies are more or less saline and that 
special precautions must be taken to neutralize the injurious effect when 
such water alone is available. Much can be done to avoid the effects of 
soil alkali through the choice of alkali-tolerant fruit crops and particularly 
the selection of stocks having this characteristic, though the roots of the 
cion may be susceptible. The importance of caution in the use of fertil- 
izers, particularly in irrigated sections, has been mentioned. 

Finally, it should be pointed out that insufficient as well as excessive 
concentrations may exist. That extremely low concentrations permit 
growth has been emphasized but it is the insufficient concentration of 
particular salts that renders the use of fertilizers necessary. 

Soil Toxicity. — The chemical composition of the soil solution must be 
considered in its effect on absorption. In this connection the presence 
of toxic substances is of great importance. The toxins may be organic 
compounds formed by bacterial activity from dead plant tissue. They 
are not, as a rule, excreted as such from plant roots, though this occurs 
under exceptional conditions, as for example when the supply of oxygen 
is deficient. Fragments of dead root hairs, roots and possibly aerial 
portions of the plant washed down into the soil, constitute the material 
acted upon by microorganisms to produce poisons. 

It must not be overlooked that bacterial activity may also produce 
compounds beneficial to plant life in so far as the products of bacterial 
action may serve as a source of food, as has been pointed out. 163 

General and Specific Effects. — The general effects of toxins are shown 
in decreased green weight and inhibited growth. The specific morpho- 
logical effects vary considerably with different substances, some producing 
more marked effects on the roots than on the green parts of the plant. 
For instance, vanillin-affected plants show decreased growth of the top 
and root growth is strongly inhibited. Dihydroxystearic acid affects 
the tops but especially the roots, the root tips becoming darkened, their 
growth stunted; the root ends are enlarged and often turned upward 
like fishhooks and their oxidizing power is strongly inhibited. Pyridine 
and picoline affect the green parts more than the roots. Cumarine- 
affected plants have stunted tops and broad distorted leaves; quinone- 
affected plants are tall and slender, with thin narrow leaves. Guanidine 
has apparently no effect on the roots, but the green parts develop small 
bleached spots which spread, the plant becomes weakened and the leaves 
break at the stem, wilt and die. 161 ' 164 



PLANT NUTRIENTS AND THEIR ABSORPTION 123 

The manner in which these toxic substances check growth is shown 
by a study of the absorption of mineral constituents. Though absorp- 
tion is always decreased, the various toxins have more or less specific 
effects. Cumarin and salicylic aldehyde depress potash and nitrate 
absorption more than phosphate absorption; quinone depresses phosphate 
and nitrate more than potash ; dihydroxystearic acid and perhaps vanil- 
lin, retard phosphate and potash more than nitrate absorption. 

Protecting Against Toxins. — The harmful effects of these toxins may 
be counteracted in numerous ways. Fertilizer treatment is efficacious; as 
might be expected, various salts act differently in overcoming the respec- 
tive effects of the toxic substances. Phosphatic fertilizers, for example, 
are most efficient in overcoming the effects of cumarin, potassic fertilizers 
in overcoming the effects of quinone and nitrogenous fertilizers in over- 
coming the effects of vanillin. 

Another way of ameliorating the effects of toxic substances in the soil 
is treatment with absorbing agents. Roots appear able to oxidize 
organic materials in such a way that their toxic properties are lost. The 
large amount of root surface which most plants have makes this oxidizing 
power important in relation to the destruction of toxic substances through 
crop rotation. 

Schreiner, Reed and Skinner 165 found that toxic solutions lost much of their 
toxicity after plants had been grown in them. They state: "The vanillin 
solution, for example, was so reduced in toxicity that a solution originally con- 
taining 500 parts per million was no more toxic to the second set of plants than 
a solution of 50 parts per million was to the first. It has been found that an 
equal number of wheat plants can remove in a similar length of time not more 
than 30 to 50 parts per million of nitrates from solution and there is no reason 
to believe that toxic substances should be removed at a much more rapid rate." 

Breazeale 18 reports that peat extract in dilute concentrations (20 parts 
per million) and calcium carbonate protect citrus seedlings against the 
toxicity of distilled water, usually associated with the presence of small 
amounts of copper. Sodium carbonate on the other hand augments the 
toxicity of soluble organic matter. 

Thus, "When soluble organic matter which is acid in reaction and stimulating 
to citrus seedlings in concentrations up to 1,000 parts per million or more is added 
to a sodium carbonate solution of 400 parts per million which in itself is not 
toxic, a highly toxic solution is formed which will kill the root tips of citrus 
seedlings. This reaction appears to be of importance in connection with the 
toxicity of soils containing small amounts of sodium carbonate." 18 

Importance in the Fruit Plantation. — To just what extent organic soil 
toxins are important in the fruit plantation is not known. That they are 
of greater significance than is generally realized there can be no question. 



124 FUNDAMENTALS OF FRUIT PRODUCTION 

Most deciduous fruit crops occupy the same soil for a considerable num- 
ber of years and consequently are subject to the influence of any toxins 
that arise from the disintegration of their own leaves, rootlets or other 
dead tissues. In addition they are subject to the action of toxins that 
may arise from the growth or decay of intercrops or cover crops that are 
grown between them. 

It has been shown 89 that ordinary crop plants exert an important 
influence upon those which follow them and that this influence "seems 
not to be attributable, at least primarily, to differences in the amount of 
fertilizer nutrients removed by the crops grown before." Thus the yield 
of buckwheat following redtop, rye, buckwheat and onions was as 7:30: 
45 : 88, in a nutrient medium deficient in nitrogen but well supplied with 
other plant nutrients, even though the nitrogen removal of the preceding 
redtop, rye and buckwheat crops was as 1.00 : 2.72: 2.42. 89 The pre- 
sumption is that the differences in the yields of the second crops were due 
to the effect of toxins. 

Pickering 150 has been able by means of various field trials and pot 
experiments to eliminate the influence of one plant upon another through 
its effect on moisture and nutrient supply, soil temperature, soil reac- 
tion, texture, carbon dioxide and bacterial content and thus to deter- 
mine both quantitatively and qualitatively their mutual influence through 
toxic substances. 

He comments as follows on the results of his investigations: 

"It has now been established with a reasonable amount of certainty that the 
deleterious effect of one growing plant on another is a general phenomenon. 
By means chiefly of pot experiments . . . the following plants have been found 
susceptible to such influence: apples, pears, plums, cherries, six kinds of forest 
trees, mustard, tobacco, tomatoes, barley, clover, and two varieties of grasses, 
whilst the plants exercising this baleful influence have been apple seedlings, 
mustard, tobacco, tomatoes, two varieties of clover, and 16 varieties of grasses. 
In no case have negative results been obtained. The extent of the effect varies 
very greatly : in pot experiments the maximum reduction in growth of the plants 
affected has been 97 per cent., the minimum 6 per cent., whilst in field experiments 
with trees the effect may vary from a small quantity up to that sufficient to 
cause the death of the tree. The average effect in pot experiments may be 
roughly placed at a reduction of one-half to two-thirds of the normal growth 
of the plant, but no sufficient evidence has yet been obtained to justify the con- 
clusion that any particular kinds of plants are more susceptible than others, or 
any particular surface crop is more toxic than another; that such differences 
exist is highly probable, but all the variations observed so far may be explained 
by the greater or lesser vigour of the plants in the particular experiments in 
question. Similarly as regards the effect of grass on fruit trees, though the extent 
of it varies very greatly, and in many soils is certainly small, we must hesitate 
to attribute this to any specific properties of the soils in question ; for when soils 
from different localities (including those from places where the grass effect is 



PLANT NUTRIENTS AND THEIR ABSORPTION 125 

small) have been examined in pot experiments, they have all given very similar 
results; and this applies equally to cases where pure sand, with the addition of 
artificial nutrients, has been taken as the medium of growth." 150 Evidence 
which will serve partially to differentiate between the influence of a living plant 
and the disintegration products of its dying roots is afforded by the following: 
"... a quarter of an acre of land, over which some 15 apple trees, 20 years 
of age, were distributed, was planted uniformly with Brussels sprouts; those 
under the trees suffered to the extent of 48 per cent, in their growth ; but there 
were patches in the ground where trees had been growing until the preceding 
winter, when they had been cut down, leaving the roots undisturbed in the soil, 
and in these patches the sprouts did better than elsewhere to the extent of 12 
per cent. In other parts of the ground canvas screens had been erected, at a 
height of 6 feet above the surface, to simulate, and even exaggerate, the shading 
of the trees, and under these the sprouts gave exactly the same values as on the 
unshaded ground. Thus, the trees themselves materially injured the crop, 
though the soil under the trees was more fertile than elsewhere, and though 
the shading was inoperative." 150 

The degree of susceptibility of the apple tree to the toxic influence of 
some other plant is indicated by Pickering's 150 statement that the color of 
the fruit may be materially affected "in cases of trees weighing about 2 
hundredweight when only 3 to 6 ounces of their roots extended into 
grassed ground." 

Though, as stated already, data are not available for the accurate 
•estimation of the importance of organic toxins in fruit production, the 
limited data are very suggestive. 

In commenting upon the investigations that have just been cited and on 
others of a similar character Alderman 3 remarks: "Do they not at least open to 
some question many of our preconceived ideas bearing upon plant growth and 
plant nutrition? . . . Do they not raise a question as to the arrangement of 
many crop rotations (e.g., of cover crops or other intercultures) which were 
originally worked out with the economic convenience of the grower in view rather 
than the growth reactions of the plants under consideration? ... If it is true 
in Rhode Island that onions will yield 412 bushels per acre following redtop and 
only 13 bushels following cabbages, it is probably true elsewhere and the place 
of the onion in the cropping system of the truck grower deserves the most serious 
study. If grass affords direct injury to apple trees growing in shallow soils 
underlaid with an impervious stratum of subsoil, it is probably as offensive in 
North America as in England. The writer and others interested in plant nutri- 
tion have repeatedly pointed out the difference in reaction to fertilizers between 
orchards in sod and those under cultivation. It has been generally believed that 
this difference was due to soil exhaustion of important plant food material or to 
an influence on moisture supply but the work of Pickering is a direct challenge 
to such a belief. Perhaps it is not important to the grower of fruit to know 
whether an application of nitrate of soda to a sod orchard is beneficial because 
it supplies some element of plant food material heretofore lacking or because it 



126 



FUNDAMENTALS OF FRUIT PRODUCTION 



hastens the change of toxic substances to harmless or beneficial materials, but it 
is extremely important to the investigator for it strikes back to a fundamental 
problem in plant nutrition." 

The whole question of the interrelationship of plants in the orchard 
still needs thorough investigation. 

Antagonism. — Beside organic poisons, certain inorganic salts may 
have toxic effects; for example, magnesium compounds may become 
injurious to the higher plants. The toxic action of magnesium is modified, 
however, by calcium because of the antagonism between these two ele- 
ments. Salts of either calcium or magnesium by themselves tend to 
increase the permeability of protoplasm more than a mixture of calcium 
and magnesium salts in proper proportion. Therefore, the action of 
calcium in offsetting the toxic effect of the magnesium probably is due 
to diminished magnesium absorption when both elements are present in 
suitable proportion. Antagonism occurs also between calcium and 
potassium and many other salts. 

Aeration. — In the absence of aeration roots are unable to function prop- 
erly and toxic substances are secreted. Moreover poor aeration favors 
the formation of toxins by bacteria and in the absence of an adequate 
supply of oxygen, numerous soil bacteria reduce nitrates, utilize the oxy- 
gen and leave gaseous nitrogen which is not available to the higher plants. 

The physical character of the soil has an important effect on aeration; 
stiff, retentive clays, for example, do not drain as well as sandy soils; 
consequently they are usually not so well aerated. The application of 
lime or organic fertilizers to such clays may render them mellow, better 
drained and more readily cultivated. 

Selective Absorption. — Within certain limits, plants are able to 
absorb larger amounts of one mineral constituent at their disposal than 
of another and in this way to exert a selective action. This is strikingly 
shown by Table 15, which compares the percentage composition of the 
ash of duckweed with the water in which it grew. 

Table 15. — Analyses of Ash of Duckweed and of the Mineral Matter Con- 
tained in the Water in Which It Grew 104 





K 2 


Na 2 


CaO 


MgO 


Fe 2 3 


P 2 6 


SO 3 


Si0 2 


CI 


Duckweed 

Water 


18.29 
5.15 


4.05 
7.60 


21.86 
45 . 55 


6.60 
16.00 


9.57 
0.94 


11.35 
3.42 


7.91 
10.79 


16.05 
4.23 


5.55 
7.99 



This selective ability of the plant may be explained by greater action 
on certain constituents which are thereby rendered osmotically inactive 
within the plant. This leads to further absorption of these particular 
constituents. However, selective action has definite limits and plants 



PLANT NUTRIENTS AND THEIR ABSORPTION 127 

absorb a certain amount of any constituent which is present in an 
available form and to which the protoplasm is permeable. Thus, salt 
marsh plants contain relatively large amounts of sodium chloride which 
may raise the osmotic concentration of their cell sap, but is of no 
apparent nutritive value. Similarly plants grown in nutrient solutions 
absorb whatever salts are present in solution, though the rate is greatest 
and growth best when the nutrient substances are available to the plant 
in a ratio corresponding to that in which they are utilized. 

Investigations by Schreiner and Skinner 161 bearing on this subject are very 
suggestive: "In this study the growth relationships and concentration differ- 
ences were observed between solution cultures in which the phosphate, nitrate 
and potash varied from single constituents to mixtures of two and three in all 
possible ratios in 10 per cent, stages. The better growth occurred when all these 
nutrient elements were present and was best in those mixtures which contained 
between 10 and 30 per cent, phosphate; between 30 and 60 per cent, nitrate; 
and between 30 and 60 per cent, potash. The growth in the solutions containing 
all three constituents was much greater than in the solutions containing two 
constituents, the solutions containing the single constituents giving the least 
growth. The concentration differences noticed in the solutions were also very 
striking, the greater reduction in concentration occurring where the greatest 
growth occurred. The change in the ratios of the solutions and the ratios of 
the materials that were removed from the solutions showed that where greatest 
growth occurred, as above outlined, the solutions suffered the least change 
in ratio, although the greatest change in concentration occurred. The more the 
ratios in these solutions differed from the ratios in which the greatest growth 
occurred, the more were the solutions altered in the course of the experiment, 
the tendency in all cases seeming to be for the plant to remove from any and all 
of these solutions the ratio which normally existed where greatest growth occurred, 
but was hindered in doing so by the unbalanced condition of the solution. The 
results show that the higher the amount of any one constituent present in the 
solution, the more does the culture growing in that solution take up of this 
constituent, although it does not seem able to use this additional amount 
economically." 

Similarly surpluses of lime in plants are not uncommon. 124 A part 
of the lime may be precipitated as calcium oxalate, or in some plants 
as calcium carbonate, of which cystoliths are largely composed. 

Transpiration. — The ash content of plants varies considerably under 
different conditions of soil water, available salt supply and temperature. 
Data have been reported 108 indicating that increased transpiration 
does not increase the ash absorption of plants growing in soil. For 
this reason conclusions from experiments involving nutrient solutions 
should be applied to field conditions with extreme caution. Transpira- 
tion and the absorption of nutrient salts are largely independent of each 
other. 



128 FUNDAMENTALS OF FRUIT PRODUCTION 

Schreiner and Skinner 103 discuss this subject as follows: "Many writers in 
agricultural literature seem to be under the impression that the only way that a 
plant can get the nutrients from a solution is to use all the water it can in building 
tissue and to lose the remainder by transpiration, so as to obtain the necessary 
nutrients dissolved in the soil water or nutrient solution. In other words, that 
the plant maintains a current of water entering at the root as the nutrient 
solution and leaving the plant "as pure water at the leaf surfaces, that is, by 
transpiration or evaporation. From their arguments it follows that if a half 
strength solution is presented to the plant it will have to take up and transpire 
twice as much water to obtain the same nutrients. In other words, the plant 
is supposed to absorb the mineral constituents in the same concentration as the 
solution in which the roots bathe. This is, however, not in accordance with 
the facts. The plant has greater difficulty in obtaining the mineral elements from 
the weaker solution, but it does not accomplish this by expending the extra energy 
involved in transpiring double the amount of water. 

"For instance, the loss of water from a 250-cubic centimeter [nutrient] 
solution during this 3-day period is only about 10 per cent., whereas the analysis 
of the solution after supplying this water showed the mineral nutrients to be 
reduced from 80 to as low as 23.8 parts per million, or a decrease of 70 per cent. 
It is obvious that the plants have taken the nutrients faster than the water, and 
this under conditions of good growth. 

' ' Not only does the absorbing power of the root enable the plant to take more 
nutrients per cubic centimeter of water absorbed than is contained in the same 
volume of the soil solution, but it also enables the plant to obtain a different 
ratio of the mineral nutrients for its use than exist in the nutrient solution. 

"These facts are extremely important, as they show that the absorbing power 
of the plant is not regulated by the amount of transpiration, but rather by the 
life processes within the plant and the requirements of these life processes." 

THE NUTRIENT REQUIREMENTS OF CROP AND FRUIT PLANTS 

Typical crop plants and typical deciduous fruits make distinctly 
different demands upon the soil. For most crops the soil should not be 
acid and the nitrogen requirement is relatively low. For most fruit 
trees, soil acidity, unless very high, is not a factor of concern and the 
demands for nitrogen are great. It is suggested that this more or less 
characteristic difference which requires agronomists and horticulturists 
to adopt correspondingly different attitudes on the problem of soil 
productivity is connected with the different ecological habits of these 
plants, together with the type of crop desired. Cereal crops in particular 
are adapted to an early stage in ecological succession which has not 
proceeded beyond an association where grasses are dominant. Humus 
has not yet collected in great amount; hence, crops flourish in soils of low 
acidity and require relatively little nitrogen (though they may do equally 
well or better in soils abundantly supplied with it). Fruit trees belong to 
a much later stage in an ecological succession which has reached an 
association of forest trees and in which the character of the soil has 



PLANT NUTRIENTS AND THEIR ABSORPTION 129 

been affected by previous plant associations that have grown on it. 
Humus is therefore more abundant and the plants are adapted to soils 
of relatively high acidity and great nitrogen content. Hence, lime 
is most useful for crops and nitrogen the fertilizer most often required by 
fruit trees. It is more profitable to grow cereal crops on the great plains, 
prairies, savannahs and pampas while fruit trees thrive best in the regions 
of coniferous and deciduous forests. 

Summary. — The various mineral elements and nitrogen are absorbed 
by the plant from the soil solution. These mineral elements, except a 
portion of the sulphur, may be recovered in the ash of the plant. In 
addition to the necessary mineral elements, the ash generally includes 
small quantities of a number of non-essential elements occurring in the 
soil solution. The ash content of plants varies with the kind of plant 
and with the soil upon which it is grown. The ash content of different 
tissues also varies with the kind of tissue, its age and the season. Nutri- 
ent elements must not only be in solution but must be in an available 
form — that is, combined with certain other elements and in certain 
compounds. Nitrogen is absorbed mainly as nitrates. The nitrate 
supply in the soil is subject to great fluctuations, depending on tem- 
perature, moisture, aeration, bacterial activity, the supply of nitrogen- 
carrying materials from which nitrates can be formed and many other 
factors. An important part of the orchard soil fertility question consists 
in maintaining a liberal supply of nitrates in the soil during the growing 
season. Most crop plants prefer a soil practically neutral in reaction. 
Deciduous fruits are distinctly acid tolerant and certain of them thrive 
best in an acid soil. The best orchard cover crops are likewise acid 
tolerant. The chlorotic conditions frequently found in strongly cal- 
careous and manganiferous soils apparently are due to iron starvation 
incident to an alkaline reaction. Many organic disintegration products 
are known to be toxic to certain crop plants and there is evidence that 
they are often of considerable importance in determining the produc- 
tivity of orchard soils. Some of the injurious effects of sod upon trees 
evidently are due to these toxins in the grass land. Excessive concen- 
trations of certain salts, particularly of sodium and potassium, are toxic to 
orchard trees and give rise to the so-called "alkali" conditions. Treat- 
ment for disorders of this kind may be both remedial and preventive. 
Optimum conditions for absorption are provided when the various 
nutrient elements are found in the soil solution in certain rather definite 
proportions. Sometimes harmful influences result when these ratios 
do not obtain. Both transpiration and soil aeration influence somewhat 
the rate of absorption. Within certain limits plants are able to absorb 
from the soil solution the elements most necessary, taking them out in 
proportions sometimes very different from those in which they exist. 



CHAPTER VIII 

INDIVIDUAL ELEMENTS 

The intake of nitrogen and mineral constituents in inorganic form 
has been described. Their incorporation into the plant is now considered 
with particular reference to orchard or fruit plants. In the study of 
nitrogen content analyses are expressed in percentages of fresh weight or 
of dry weight or in the absolute amounts present in a certain tissue such 
as 100 leaves; ash analyses are given in percentages of fresh weight or 
of dry weight, in percentages of total ash or in absolute amounts. 
Careful distinction should be made between determinations expressed 
in these different terms since they are not comparable. For example, 
during the development of a tissue — say the leaf — some ash constituent 
may decrease in terms of percentage of total ash, remain constant in 
percentage of dry weight and increase in absolute amount. Absolute 
amounts are particularly valuable data and show the actual changes 
in the amount of substance present. Percentages of dry weight will 
indicate the same changes provided there is no increase or decrease 
in the absolute dry weight. If there is, then these changes must be 
taken into consideration. Expression of percentage in terms of fresh 
weight involves in addition changes in the water content. Percentages 
of total ash show the relative proportions of the various ash constituents. 
Each of these determinations has its value, but each expresses different 
relations. 

NITROGEN 

Nitrogen enters the roots from the soil solution as a salt of nitric acid, 
such as potassium or sodium nitrate, or sometimes as ammonia. The 
supply of nitrates in the soil varies with temperature and moisture, 
usually being greatest in late spring and early autumn, but persisting 
throughout the summer. 

Synthesis of Organic Nitrogenous Compounds. — Most of the inorganic 
nitrogen absorbed is carried up the trunk and branches to the leaves 
where it is elaborated into amino-acids and other nitrogenous organic 
compounds. The elaboration of nitrates to amino-acids takes place for 
the most part in the chloroplasts of the leaf mesophyll cells. Light has 
been shown 117 to increase nitrogen assimilation, blue-violet and ultra- 
violet light being particularly effective. Light from the blue end of the 
solar spectrum is relatively stronger in cloudy weather; light from the 
other end of the spectrum which is the more important for the photo- 

130 



INDIVIDUAL ELEMENTS 131 

synthetic process, predominates in direct sunlight. According to one 
investigator 191 the influence of light in favoring protein formation and 
the elaboration of inorganic to organic nitrogenous compounds becomes 
more pronounced as the stage of development advances. Nitrogen 
elaboration can take place in the absence of chlorophyll and light, in 
which case presumably carbohydrates are used. 208 The amino-acids 
which are the first products of elaboration are either used directly in 
the leaf or are conducted through the phloem to all parts of the plant 
where they are used in the building up of every nitrogen-containing 
organic compound found in plants as well as of certain nitrogen-free 
organic substances (essential oils, resins and polyterpenes). The amino- 
acids are combined to form the proteins which occur in all protoplasm. 
Other nitrogenous organic compounds are the purines and pyrimidines 
which enter into the composition of nucleic acids, nucleins and nucleo- 
proteins, substances characteristic of the cell nucleus. Lecithins and 
chlorophyll contain nitrogen. Nitrogen-containing compounds which 
are not of universal occurrence are the alkaloids, ptomaines, amines, 
cyanogenetic glucosides and indican (natural indigo blue). 

Translocation and Use of Elaborated Nitrogenous Compounds. — The 
elaboration of nitrates to amino-acids beginning at the time the leaves 
are well developed, proceeds as long as they remain green, reaching a 
maximum when temperature, light and soil supply conditions are at an 
optimum. The elaborated nitrogen-containing compounds are con- 
stantly passing out of the leaves throughout the season of elaboration as 
fast as they are made. They are used for new tissue development, for 
shoot growth, new leaves, increments to branches, trunks and roots, new 
roots and especially for fruit and seed development. A considerable part 
of the remainder is stored in the phloem. Storage is particularly rapid 
in the fall when growth has ceased and before the leaves are separated 
from the plant by abscission layers. 

New tissue growth in early spring is at the expense of stored foods, 
including stored nitrogen. This reserve supplies the developing shoots, 
leaves, flowers, rootlets, much of the new tissue in trunk, branches and 
roots and the fruit in its initial stages. Hence for good spring growth of 
tissues, especially shoots, leaves and spurs, abundant nitrogen storage the 
previous season is a prime requisite. This, in turn, depends on a 
good supply of available nitrogen in the soil between June 1 and Sept. 15 
or Oct. 15, a supply more than sufficient for fruit and tissue development. 
Summer defoliation or a diseased condition of the leaves evidently checks 
growth the following year by cutting down the supply of stored and elabo- 
rated nitrogen. 

Attention should be called to the apparent usefulness of unelaborated 
nitrogen to the apple and pear tree and probably to other fruits, through 
enabling them to set a larger crop. It is a common experience to secure 



132 



FUNDAMENTALS OF FRUIT PRODUCTION 



a good set of fruit when liberal applications of some readily available 
nitrogen-carrying fertilizer, such as nitrate of soda, are made to weak 
trees just before blossoming, though without such applications these 
same trees would bloom heavily but set little or no fruit. This response 
by the tree is obtained within 2 or 3 weeks after application of the fer- 
tilizer and at a season when there is practically no leaf area to build up 
elaborated foods. It would seem, therefore, that the synthesis of organic 
nitrogenous compounds can take place in tissues other than the leaves. 

Seasonal Distribution of Nitrogen. — A study of the seasonal variation 
in nitrogen content of different parts of the plant gives a perspective of 
the processes of nitrogen elaboration, storage and utilization. 






2 






W O Q) 

< <■ If) 



\n 



Fig. 11. — Nitrogen content of plum leaves in percentages of dry weight. (Plotted from 

data given by Richter. 155 ) 



In Leaves. — Since the leaf is the principal organ of nitrogen elaboration the 
seasonal distribution of this element in the leaf is important. Leaf buds have a 
high percentage of nitrogen; certain analyses show 3.687 per cent, of the dry 
weight in the cherry and 3.779 per cent, in the plum. 155 Fruit buds have a 
slightly higher percentage composition in nitrogen, corresponding analyses 
showing 3.771 per cent, in the cherry and 4.142 per cent, in the plum. 155 

Table 16 shows the decrease in percentages of nitrogen in apple, pear and 
cherry leaves from May to October. 155 This is shown even more clearly by the 
graph in Fig. 11. The accompanying composite table (Table 17) is a good 
illustration of the steady decrease in the percentage nitrogen content of plum 
leaves. Though there is a continuous decline in the percentage of nitrogen from 
May through October, there are two periods of rapid decrease, one in May and 
the other in September. Between the periods of rapid decrease the percentage 
composition of the leaf is fairly constant. The first period of decrease is at the 
time when the leaf is growing rapidly and the available nitrogen supply is limited, 
because of rapid and simultaneous shoot, wood and root development. The 
period of relatively constant nitrogen content occurs when nitrogen intake is 



INDIVIDUAL ELEMENTS 



133 



Table 16. — Nitrogen in Leaves of Apple, Pear and Cherry 155 
(In percentage of dry weight) 



Apple 


Pear 


Cherry 


May 9, 14 

June 22 


4.152 
2.628 
2.015 
1.198 


4.087 
2.782 
2.041 
0.917 


4.867 
2 639 


Aug. 29 

Oct. 2, 15 


2.160 
1.022 



Table 17. — Nitrogen of Plum Leaves 155 
(In percentage of dry weight) 

May 18, 1908 4.917 Aug. 21, 1909 2.402 

May 27, 1907 3.809 Aug. 29, 1908 2.398 

June 22, 1908 2.208 Sept. 6, 1909 2.413 

July 14, 1909 2. 917 Sept. 30, 1908 1 . 152 

July 31, 1909 2.816 Oct. 28, 1909 1.096 

very nearly balanced by the demands for new vegetative tissue and for the develop- 
ment of the fruit and seed. The second period of decrease indicates rapid deple- 
tion of the nitrogen content of the leaf, the withdrawal being much in excess of 
the, amount supplied. This picture presented by the plum is fairly typical of 
other deciduous fruits. 

On the other hand, the absolute amount of nitrogen in the leaves does not 
decrease throughout the season. Table 18, showing grams of nitrogen in 100 
apple, pear, cherry and plum leaves from July to October, brings this out clearly 
and shows that the absolute nitrogen content of leaves does not decrease 
materially until after September. In all probability it is increasing until August. 



Table 18. — Grams of Nitrogen in 100 Leaves 155 



Apple 



Pear 



Cherry 



Plum 



July 14 

July 31 

Aug. 18, 21.... 
Sept. 3, 4, 6. .. 

Oct. 7 

Oct. 23, 27, 29. 
Nov. 4 



0.704 
0.734 
0.795 
0.742 



. 232 



0.401 
0.421 
0.409 
0.368 

0.121 



0.713 
0.553 
0.624 
0.593 
0.602 
0.178 



0.555 
0.477 
0.376 
0.389 

0.180 



A comparison of the data showing absolute nitrogen content with the data 
showing percentage composition of the dry weight indicates that in young leaves 
with their high percentage of nitrogen, growth and carbohydrate formation 
proceed at such a rate as to reduce the percentage composition of nitrogen even 
though the intake of nitrates during this period is greater than the outgo of 
elaborated nitrogen. During July and August and sometimes later, the leaf 



134 



FUNDAMENTALS OF FRUIT PRODUCTION 



supplies the branches with an amount of elaborated nitrogen about equal to the 
amount of nitrates taken in. From September on, however, the leaves receive 
less nitrate in proportion to the elaborated nitrogen which passes back into the 
branches; consequently the percentage nitrogen content of the leaf is cut in 
half and only one-third the amount the leaves once contained remains in them 
when they fall. 

In Branches, Trunks and Roots. — A study of the seasonal variation in the 
content of various parts of a tree shows what becomes of the nitrogen that passes 
out of the leaf. Table 19 shows the distribution of nitrogen in a 7-year old apple 
tree at different seasons. Nitrogen content is expressed in percentages of dry 
weight. 

Table 19. — Seasonal Changes in the Nitrogen Content of a 7-year Old 

Apple Tree 23 

(Percentages of dry weight) 





Dormant, 
Dec. 3 


Buds 

swelling, 

Apr. 20 


In bloom, 
May 18 


Active 

growth 

over, 

July 12 


Leaves 
falling, 
Oct. 12 


Summer's growth 

1-year old branches 

2-year old branches 

3-year old branches 

4-year old branches 

5-year old branches 

Trunk 


0.80 
0.63 
0.42 
0.40 
0.39 
0.23 
0.41 
0.79 


1.01 
0.68 
0.62 
0.41 
0.32 
0.32 
0.47 


0.69 
0.38 
0.32 
0.29 
0.28 
0.27 
0.46 


0.64 
0.40 
0.32 
0.27 
0.24 
0.23 
0.22 
0.28 
0.48 


0.61 
0.57 
0.50 
0.37 
0.30 
0.25 
0.24 


Large roots 


0.31 


Small roots 


0.78 


0.70 


0.77 













These figures bring out two important points — first, that the younger the 
tissue the greater is its nitrogen content and second, that practically all tissues 
have a minimum when active growth has ceased and a maximum at the time of 
bud swelling. The increase in all tissues, except leaves, during the fall indicates 
nitrogen storage. The nitrogen that is stored over the winter evidently comes 
from the leaves. 

Reference to the last table shows that in two places only is there a decrease 
in the percentage of nitrogen before bud swelling, namely, in the smaller roots 
and in the 5-year old branches. The decrease in the roots probably is due to 
their beginning to function and to renew growth earlier in the spring than do the 
tops. 

In Spurs. — The seasonal changes in the nitrogen content of bearing, non- 
bearing and barren spurs from mature apple trees is shown in Fig. 12. 
The variations in non-bearing spurs, or more accurately productive spurs in the 
off year, are similar to those in the roots, trunks and branches with a maximum 
in March at the time of bud swelling and a minimum at the end of June when 
growth is over. 100 Barren spurs have a lower nitrogen content throughout the 



INDIVIDUAL ELEMENTS 



135 



year and there is little evidence of accumulation in the fall; this may be associated 
with the absence of fruit bud differentiation in these spurs. 

Bearing spurs are peculiar, however, in that their nitrogen content increases 
after the buds have broken, though in all other tissues of spur-bearing trees it 
decreases when the plant is in bloom. This indicates that though the vegetative 
tissues use locally stored nitrogen with the result that their nitrogen content 
decreases, the blossoming spurs draw on a general supply and later upon the new 
supply of the current season with the result that their nitrogen content is aug- 
mented up to the time of fruit setting. This reserve supply is located probably 
in the phloem, for a marked decrease in the nitrogen content of bark has been 
found in many plants.' In Rhus elegans for example the bark has been found 




Fig. 12. — Nitrogen content of apple spurs in percentages of dry weight, bearing spurs 
represented by continuous lines marked W, B and J for Wealthy, Ben Davis and Jonathan 
respectively; non-bearing spurs shown by broken lines marked B and </; barren spurs 
represented by dot-dash lines marked B and N for Ben Davis and Nixonite. {After 
Hooker. 100 ) 



to contain 1.52 per cent, of nitrogen in the winter and only 0.36 per cent, in the 
spring. Similarly in the bark of Acer platanoides 26 per cent, of the stored 
nitrogen disappeared from winter to spring; in the bark of the cherry 37.16 per 
cent, and in the red beech- 30 to 50 per cent, disappeared during shoot growth. 

The nitrogen that is moved from the bark into the blossoming spur passes on 
into the developing fruit, so that in the biennially bearing spur the nitrogen 
content decreases as long as the fruit is attached. Murneek 90 has shown recently 
that the total nitrogen content of apple spurs is proportional to the leaf area and 
that it decreases as a result of defoliation. 

In Fruit. — Though the nitrogen of the fruit, measured in percentages of dry 
weight, decreases throughout development on account of the increment in dry 
matter, the absolute amount present increases continuously. Table 20 shows 
the nitrogen content of apples in percentages of dry weight and in absolute 
amounts. 



136 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 20. — Nitrogen Content of Developing Apples 149 



White Astrakan 


Pleissner Rambour 


Date 


Percent- 
age of dry 
weight 


Grams in 
1,000 fruits 


Date 


Percent- 
age of dry 
weight 


Grams in 
1,000 fruits 


May 29 

June 8 

June 18 


3.28 
2.20 
1.57 
1.21 
0.71 
0.51 
0.29 
0.37 
0.58 
0.23 


0.87 
3.81 
9.75 
14.70 
15.00 
19.00 
16.60 
28.60 
23.40 
16.80 


June 2 

June 12 

June 22 

July 2 

July 12 

July 22 

Aug. 1 

Aug. 11 

Aug. 21 

Aug. 31 

Sept. 10 

Sept. 20 

Sept. 30 


3.65 
2.78 
1.76 
1.26 
1.48 
0.54 
0.65 
0.63 
0.56 
0.39 
0.61 
0.66 
0.47 


1.12 

5.76 

11.40 


June 28 


19.70 


July 8 

July 18 

July 28 


52.20 
34.20 
56.00 


Aug. 7 

Aug. 17 

Aug. 27 


73.60 
59.20 
62 . 40 
91.20 
114.00 
86.40 



An examination of the graphic presentation in Fig. 13 of the increase in the 
absolute nitrogen content of apples and pears shows that the increase is rapid 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

°26 6 15 25 5 15 25 4- 14 24- 3 13 23 3 
May June July Aug. Sept Oct. 

Fig. 13. — Grams of nitrogen in one thousand fruits of the apple shown by broken lines 
and of pears shown by continuous lines. (Plotted from data given by Pfeiffer. 149 ) 

at first, that in August there is little or no change and that in September in two of 
the apple varieties, there is a second period of increase. These periods of increas- 

























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INDIVIDUAL ELEMENTS 



137 



ing nitrogen content correspond to those seasons when temperature and moisture 
conditions are such as to favor nitrification in the soil. 

The percentage nitrogen content of young fruit is very high. So also is that 
of the seed, to which in fact the nitrogen content of the young fruit is in large 
part due. In terms of dry weight, the nitrogen content of apple seeds has been 
found to be 3.17 per cent.; of almonds 4 per cent.; of coffee {Coffea arabica) beans 
1.96 per cent.; and of cocoanuts 1.65 per cent. 38 

In Various Tissues of Trees of Different Age. — A study of the nitrogen content 
of trees of various ages will round out the picture of nitrogen distribution. 

Table 21 shows the percentages of nitrogen in the leaves, new growth, trunk, 
roots and fruit of apple trees of ages ranging from 1 to 100. Since the material 
was collected from various sources, the analyses are not strictly comparable, 
though they are suggestive. 



Table 21. — Analyses of Apple Trees 
(1 to 9 from Thompson, 186 13 and 100 from Roberts, 157 30 from Van Slyke 190 ) 
A Nitrogen in percentage of dry weight. B Absolute amounts of nitrogen in 
grams. 



Age 


Leaves 


New growth 


Trunks and 
branches 


Roots 


Fruit 




A 


B 


A 


B 


A 


B 


A 


B 


A 


B 


1 


1.71 


0.44 






0.30 


0.29 


0.39 


0.20 






2 


2.09 


1.51 






0.57 


1.36 


0.88 


1.14 










3 


2.36 


2.08 






0.52 


4.00 


0.73 


3.29 










4 


1.66 


2.24 






0.45 


6.35 


0.59 


2.99 










5 


1.76 


7.84 


0.89 


1.93 


0.48 


17.20 


0.64 


9.85 










6 


1.74 


10.50 


0.94 


2.41 


0.39 


16.60 


0.62 


17.70 










7 


1.45 


13.60 


0.84 


3.66 


0.45 


30.55 


0.64 


26.10 





35 


4 


34 


8 


1.74 


41.00 


0.93 


6.06 


0.36 


45.30 


0.62 


47.70 





43 


5 


93 


9 


1.70 


61.50 


0.82 


9.08 


0.35 


85.50 


0.58 


81.00 





31 


10 


55 


13 


1.85 


131.50 























30 


2.09 
1.04 


394 . 00 
435 . 00 


0.95 
1.04 


13.60 
390.00 













31 


258 


no 


100 


0.27 


2863 . 00 


0.22 


417.00 





These figures show that the young tree is specially rich in nitrogen. The 
roots have a higher percentage content than the trunk, but a lower content than 
the new growth. The percentage nitrogen content of both roots and trunk falls 
to a very low level in the 100-year old tree, due to the great preponderance of 
woody tissue. That of the leaves was estimated from samples collected in the 
fall and consequently is probably too low, except in the case of the 100-year old 
tree, where the sample was taken in July. 

The most striking observation to be made concerns the large proportion of 
the total nitrogen of the plant that is in the leaves, roughly about one-fourth in 
trees up to 9 years of age. Since these figures represent the amounts at leaf fall, 
even larger amounts must be present in the leaves during the summer. 



138 



FUNDAMENTALS OF FRUIT PRODUCTION 



From the data available it is impossible to say how much of the nitrogen of 
the trunk is stored and how much is a permanent part of its tissues. Hence any 
attempt to calculate the amount taken up yearly from the soil would be guess- 
work. However, it is interesting that in a 30-year old tree, two-thirds as much 
nitrogen goes into the crop as falls with the leaves and the amount used for new 
growth is insignificant in comparison. 

Similar relationships hold for fruits other than the apple as Table 22 shows. 

Table 22. — Pounds of Nitrogen in Parts of a Full Grown Tree 190 



Apple 



Peach 



Pear 



Plum 



Quince 



Fruit or fruit pulp. 

Stones 

Stems 

Leaves 



New growth 



0.57 


0.12 


0.08 


0.08 




0.03 




0.02 
0.01 


0.87 


0.52 


0.15 


0.12 


0.03 


0.05 


0.02 


0.02 



0.09 



0.09 
0.01 



The data presented in Table 23 show the nitrogen contents of various fruits. 
Table 23. — Pounds of Nitrogen in 1,000 Pounds of Fresh Fruit 29 



Almonds 7.01 

Apricots 1 . 94 

Apples 1.05 

Bananas 0.97 

Cherries 2.29 

Chestnuts 6.40 

Figs 2.38 

Grapes 1.26 



Lemons 1.51 

Olives 5.60 

Oranges 1 . 83 

Peaches 1.20 

Pears 0.90 

French prunes 1.82 

Plums 1.81 

Walnuts 5.41 



PHOSPHORUS 

It has been pointed out that the nitrates absorbed by the roots 
probably are carried to the leaves and there elaborated into organic nitro- 
gen-containing compounds. Though there is no direct evidence to show 
where the elaboration of inorganic phosphates to organic phosphorus- 
containing compounds takes place, the remarkable similiarity that exists 
between the variations in nitrogen and in phosphorus content of practi- 
cally all tissues, suggests that phosphorus, like nitrogen, is elaborated for 
the most part in the leaf. 

Synthesis of Phosphorus-containing Organic Compounds. — The 
amount of phosphorus assimilated is stated to be closely related to the 
amount of illumination 136 the plant receives and appears to be connected 
with photosynthetic activity. Red and yellow light have been found 
more effective than blue or violet in promoting phosphorus assimilation. 196 

Wherever phosphorus is found in organic combination it exists as 
phosphate. Thus it occurs in nucleic acids, nucleins and nucleo-proteins 



INDIVIDUAL ELEMENTS 



139 



— substances always present in the cell nucleus — in lecithins, in hexose 
phosphoric acid which is essential to zymase activity in yeast and prob- 
ably to the activity of similar enzymes in all plant tissues. The globoid 
in aleurone grains is composed of calcium -magnesium phosphate. 

Translocation and Use of Phosphorus-containing Compounds. — The 
distribution of phosphorus in the fruit tree is very similar to that of 
nitrogen. Young tissue is richer in phosphorus than older tissue, young 
leaves and young bark being particularly rich in this element and much 
the same relations hold in regard to elaboration, storage and utilization 
of phosphorus as with nitrogen. Most tissues contain approximately 
six times as much nitrogen as phosphorus. This holds roughly for 
trunk and branches, new growth, buds and young leaves. The older 
leaves have less phosphorus, the fruit and the apple spur more. The 
general constancy of the phosphorus-nitrogen ratio indicates that the 
two elements may be combined in the same molecule. Nucleins, nucleo- 
proteins and lecithin contain both elements and are of universal occur- 
rence in all living plant tissues. Table 24 shows the relative amounts of 
the various types of organic phosphorus in developing grape seeds. The 
bulk is nuclein phosphorus and should this be the case in most plant 
tissues the relative constancy of the nitrogen-phosphorus ratio would 
be explained. 



Table 24. — The Phosphorus Content of Grape Seeds 2 
(In percentages of fresh weight) 



Hard, Sept. 6 



Softening, Sept. 
30 



Ripe, Oct, 30 



Lecithin P. . . . 
Nuclein P. . . . 
HCl-soluble P 



0.0017 
0.0159 
0.0019 

0.0195 



0.0018 
0.0184 
0.0016 

0.0218 



0.0021 
0.0197 
0.0016 

0.0234 



Nevertheless distinct differences exist between the variations in the 
nitrogen and in the phosphorus content of the same tissue and these 
show that phosphorus compounds do not play the same part in plant 
metabolism as nitrogen compounds. 

If organic phosphorus-containing compounds are built up chiefly in 
the leaves, they pass out of the leaves as fast as they are made and are 
used by the developing fruit and in the growth of vegetative tissues. 
Before the leaves fall, a considerable amount of their phosphorus is 
withdrawn and stored in the phloem. The phosphorus used in the first 
stages of growth in the spring and in the initiation of fruit development is 
obtained from stored compounds. 



140 



FUNDAMENTALS OF FRUIT PRODUCTION 



Amounts Used in Fruit Production. — In general the tree may be said 
to require relatively large amounts of phosphorus for fruit production, 
much larger than for mere vegetative growth. However, analyses would 
indicate that the total amount required by the trees for the development 
of their fruits and of their new vegetative tissue would not be more than 
8 pounds per acre in a peach orchard yielding at the rate of 300 bushels; 
the total phosphorus draft of most other deciduous fruits is not materially 
greater. Considering the limited amounts of phosphorus used by decidu- 
ous fruit trees, and the comparatively large amounts present in nearly 
all soils as well as the supply in the subsoil available to deep-rooted trees, 
it is evident that under average orchard 'conditions phosphorus is not 
likely to be a limiting factor and that phosphorus fertilization is likely 
to be of little direct use in assisting tree growth or in promoting fruit 
production. On the other hand it may be of great value hi promoting 
the growth of grasses, legumes or other crops grown between the trees 
for mulching or other purposes. This subject is discussed in some detail 
under the heading of indirect methods of fertilization. 

Seasonal Distribution of Phosphorus. — There is a close similarity 
between the seasonal distribution of phosphorus and nitrogen in many 
parts of the fruit tree. 



0.5 



0.4 



0.3 



0.2 

































1 
1 
1 






1 

1 








1 
1 
1 

1 






1 
1 
1 




"1 

1 

1 

1 



Fig. 14. — Phosphorus content of plum leaves in percentages of dry weight. (Plotted 
from data given by Richter. 165 ) 



In Leaves. — Though leaf buds have a slightly higher percentage nitrogen 
content than fruit buds, they have a slightly lower percentage of phosphorus. 
The phosphorus content of the former has been found to be 0.576 per cent, of the 
dry weight in the cherry and 0.594 per cent, in the plum; of the latter, 0.570 
per cent, in the cherry and 0.592 per cent, in the plum. 155 

The young leaf has about the same high percentage of phosphorus as the bud, 
but this decreases rapidly with age as does the nitrogen, there being two periods 
of rapid decline, one in May, the other in September (see Table 25 and Figure 14). 
The ratio of phosphorus to nitrogen in the young leaf is 1 : 6. Before leaf fall 
it is 1 : 10 or 1 : 15. This indicates that the plant uses its phosphorus supply 



INDIVIDUAL ELEMENTS 



141 



more thoroughly than its nitrogen, withdrawing it more completely from tissues 
that are exfoliated and either using it immediately in tissue building or storing it. 

Table 25. — The Phosphorus Content of Leaves 155 
(In percentages of dry weight) 



Apple 



Pear 



Cherry 



Plum 



May 9, 14, 18 

June 22 

Aug. 29 

Sept. 30, Oct. 2, 15 



0.566 
0.245 
0.207 
0.126 



0.595 
0.181 
0.177 
0.069 



0.602 
0.302 
0.329 
0.273 



0.510 
0.305 
0.289 
0.197 



The absolute amounts of phosphorus in leaves of various ages are shown in 
Table 26. As with nitrogen, the total amount of phosphorus in the leaf is low at 
first, despite the high percentage, because of the small size of the leaf. It then 
increases as the leaf grows, reaches a maximum and finally declines, the decline, 
however, coming only a short time before abscission. 

Table 26. — Grams of Phosphorus in 100 Leaves 155 



Apple 



Pear Cherry 



Plum 



July 14 

July 31 

Aug. 18, 21 

Sept. 3, 4, 6 

Oct. 23, 27, 29, Nov. 4 



0.064 
0.065 
0.070 
0.060 
0.026 



0.036 
0.043 
0.034 
0.034 



0.072 
0.069 
0.068 
0.061 
0.061 



0.054 
0.049 
0.049 
0.044 



In the work from which this table is computed the possibility of loss of nutri- 
ent elements by climatic agencies was considered. Le Clerc and Breazeale 121 
called attention to the possibility that plant tissue may lose considerable amounts 
of mineral constituents through the dissolving action of rain. In this way 
apple leaves attached to the branches lost 3 per cent, of their nitrogen, 
25 per cent, of their phosphorus, 18 per cent, of their potash and 6 per cent, of 
their lime simply by washing in water. This indicates that considerable amounts 
of soluble substances exuded from the surface may be washed off the leaves during 
the period between the formation of the abscission layer and the time of actual 
leaf fall. 

In Branches, Trunk and Roots. — The percentage of phosphoric acid (P2O5) in 
the ash of sap-wood is usually higher than in bark ash; for example, in the pear it 
has been recorded as 12.62 per cent, in the sap-wood, as 2.98 per cent, in the bark 
and in the grape 7.625 per cent, in the sap-wood and 4.705 per cent, in the bark. 64 

This does not mean, however, that the bark contains less phosphorus than the 
sap-wood, for as has been pointed out, the total ash content of wood and 
especially sap-wood is much less than that of bark. The figures indicate that 
though the sap-wood contains relatively large percentages of phosphoric acid, in 
the pear and grape at least the bark contains larger absolute amounts. 



142 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 27. — The Phosphorus Content of a 7-year Old Apple Tree 23 
(Expressed in percentages of dry weight) 



/ 


Dormant, 

Dec. 3, 

1914 


Buds 
swelling, 
April 20, 

1915 


In bloom, 

May 18, 

1915 


Growth 

over, July 

12, 1915 


Leaves 

falling, 

Oct. 12, 

1915 


Summer's growth 

1-year old branches 

2-year old branches 

3-year old branches 

4-year old branches 

5-year old branches 

Trunk 

Large roots 

Small roots 


0.14 
0.11 
0.08 
0.07 
0.05 
0.04 
0.10 
0.16 


0.16 
0.11 
0.10 
0.07 
0.06 
0.06 
0.12 
0.17 


0.10 
0.0? 
0.06 
0.05 
0.04 
0.04 
0.09 
0.14 


0.14 
0.10 
0.08 
0.07 
0.06 
0.05 
0.06 
0.11 
0.14 


0.13 
0.10 
0.08 
0.07 
0.06 
0.05 
0.06 
0.12 
0.17 



Phosphorus, like nitrogen, is present in greatest amounts in the younger 
roots and branches and is at a maximum in nearly all tissues when the buds are 
swelling (see Table 27). The chief difference between phosphorus and nitrogen 




Fig. 15. — Phosphorus content of apple spurs in percentages of dry weight; bearing 
spurs represented by continuous lines, non-bearing spurs by broken lines and barren spurs 
by dot-dash lines. {After Hooker. 100 ) 

is that phosphorus reaches a minimum in most tissues in May when the tree is 
in bloom, while nitrogen does not reach a minimum until July when active growth 
is over. In all woody tissues there is an accumulation of phosphorus, as of nitro- 
gen, in the fall, indicating storage. 

In Spurs. — Figure 15 shows the seasonal variations in the phosphorus content 
of apple spurs. 100 In non-bearing and in barren spurs, the variations are similar 
to those in other woody tissues, with a minimum in May. However, in June 



INDIVIDUAL ELEMENTS 



143 



during the period of fruit bud differentiation there is a marked increase which is 
particularly pronounced in spurs differentiating fruit buds. Phosphorus accu- 
mulation in the fall is well marked, especially in productive spurs. 

In bearing spurs there is a considerable increase in phosphorus during 
blossoming, indicating that these organs draw upon a supply of stored phos- 
phorus, which may be assumed, by analogy with nitrogen, to be in the bark. 
Moreover, the phosphorus content of bark is at a maximum in the spring. 

In Fruit. — -As soon as the fruit begins to develop, the phosphorus content 
of the bearing spur decreases. At this time the spur probably is supplying the 
young fruit with phosphorus, which accumulates, to a considerable extent, in 
fruits and seeds. This increase is illustrated by the figures in Table 28 showing 
the amounts in ripening grapes. 

Table 28. — Grams of Phosphorus in 1,000 Berries of the Grape 138 

July 27 0.169 Sept. 17 0.434 

Aug. 9 0.315 Sept. 28 0.550 

Aug. 17 0.262 Oct. 5 0.619 

Aug. 28 0.206 Softening Oct. 12 0.455 Fully ripe 

Sept. 7 0.373 Oct. 22 0.320 Rotten 

In Various Tissues of Trees of Different Ages. — The percentages and absolute 
amounts of phosphorus in the tissues of apple trees of various ages is shown in 
Table 29. In general the new growth and the leaves, even at the time of leaf 
fall, are richest in phosphorus, the fruit next, then the roots; the trunk and older 
branches have the least. 



Table 29. — Phosphorus Content of Apple Trees of Various Ages 
(1 lo 9 computed from Thompson, 185 13 and 100 from Roberts, 1 * 1 30/row Van Slyke 120 ) 





Leaves 


New Growth 


Trunk and 
branches 


Roots 


Fruits 


Age 


Per cent. 

dry 

weight 


Grams 


Per cent. 

dry 

weight 


Grams 


Per cent. 

dry 

weight 


Grams 


Per cent. 

dry 

weight 


Grams 


Per cent. 

dry 

weight 


Grams 


1 
2 
3 
4 
5 
6 
7 
8 
9 
13 


0.12 
0.13 
0.14 
0.10 
0.11 
0.10 
0.10 
0.11 
0.15 
0.21 
0.13 
0.17 


0.03 

0.10 

0.13 

0.13 

0.51 

0.63 

0.90 

2.68 

5.33 

15.83 

27.70 

73.20 


0.11 
0.13 
0.11 
0.13 
0.15 

0.13 
0.16 


0.24 
0.34 
0.47 
0.82 
1.64 

2.00 
61.40 


0.03 
0.07 
0.07 
0.06 
0.05 
0.04 
0.06 
0.05 
0.08 

0.04 


0.03 
0.17 
0.50 
0.80 
1.96 
1.85 
4.14 
6.03 
19.15 

705 . 00 


0.03 
0.10 
0.11 
0.06 
0.06 
0.07 
0.06 
0.07 
0.09 

0.04 


0.02 
0.13 
0.47 
0.31 
1.00 
1.99 
2.48 
5.33 
12.62 

83.00 







08 
08 
07 


1 

1 
2 


o: 

4- 
3J 


i 

i 


30 

100 


0.6 


49 


(X 


) 















Of particular interest is the comparison of the absolute amounts of phosphorus 
in the fruit and leaves with the nitrogen content of these tissues. In a 30-year 
old tree in full bearing more phosphorus is lost with the crop of fruit than falls 
with the leaves, even if it be assumed that 25 per cent, of the original amount was 



144 



FUNDAMENTALS OF FRUIT PRODUCTION 



removed by the dissolving action of rain. This is true of many fruit trees, as 
Table 30 shows. 189 This relation does not hold for young trees just in bearing. 
That more phosphorus is lost in the crop than with the leaves of mature trees 
may be attributed to several factors. As has been emphasized, only one-tenth 

Table 30. — Pounds of Phosphorus in Parts of a Full Grown Tree 190 





Apple 


Peach Pear 


Quince 


Plum 


Fruit or pulp 

Stones 

Leaves 


0.105 

0.061 
0.004 


. 026 
0.004 
0.031 
0.004 


0.013 

0.008 
0.004 


0.017 

0.004 
0.004 


0.013 
0.004 
0.008 


New growth 


0.004 











to one-fifteenth as much phosphorus as nitrogen is left in the leaf, but the fruit 
contains one-fifth as much phosphorus as nitrogen. This in turn may be cor- 
related with the finding that the phosphorus content of leaves on peach trees 
in heavy bearing is less than that of the leaves on trees bearing a small crop. 19 ' 4 

Table 31. — Phosphorus Content of Peach Leaves in Bearing and Non-bearing 

Years 194 
(Percentage of dry weight) 

First four years . 30 

Five years of bearing . 24 

1904 (no crop) 0.29 

The data in Table 29 suggest that this may hold for the apple as well as the peach. 
Table 32 gives the phosphorus content of various fruits in absolute amounts. It 
is present in seeds in greater amounts. 

Table 32.— Pounds of Phosphorus in 1,000 Pounds of Fresh Fruit 29 



Almonds 0.45 

Apricots . 29 

Apples 0.14 

Bananas . 07 

Cherries 0.31 

Chestnuts '. 0.52 

Figs 0.38 



Lemons . 25 

Olives 0.55 

Oranges 0.23 

Peaches . 37 

Pears . 15 

French prunes . 30 

Plums 0.33 



Grapes 0.05 Walnuts 0.65 

POTASSIUM 

Though the history of potassium in a fruit tree like the apple is in 
many respects similar to that of phosphorus, there are important 
differences. 

Synthesis, Translocation and Use of Potassium-containing Com- 
pounds. — It is not known where potassium is elaborated and there is no 
evidence to show that the inorganic potassium taken from the soil by 
the roots is combined in organic form in the leaves to any greater extent 
than in any other part of the plant. In just what form of organic com- 
bination potassium is necessary for the proper activity of the plant is also 



INDIVIDUAL ELEMENTS 145 

unknown. However, certain proteins crystallize as potassium salts; 
sinigrin is myronate of potash. Complex salts of calcium, magnesium 
and potassium are not uncommon. Gum arabic contains a calcium- 
magnesium-potassium salt of arabic acid. 

During the winter, potassium is stored in both the sap wood and bark 
and in older branches than nitrogen or phosphorus. In the spring, it is 
translocated and used in the development of new tissue, but preeminently 
for fruit and then for leaves. Heavy crops reduce the potassium content 
of the leaves and much more potassium goes into the fruit than is lost 
with the leaves. In general wherever potassium is present in large 
amounts as in seeds and in young tissue, calcium is present in small 
quantities and wherever there is a small amount of potassium, calcium is 
present in large amounts. 

The Demand and the Supply. — In one way or another the idea has 
gained credence that fruit trees make heavy demands on the soil for 
potash and consequently that potash is one of the most necessary in- 
gredients in fertilizers for orchards. Indeed, so firmly has this idea 
become established that '/Fertilize trees with nitrogen for wood growth 
and with potash for fruit production" is a time-honored recommendation 
in the literature of fruit growingy It has also been a rather general 
opinion that potash mainly is responsible for the red coloration of fruits 
and that consequently potash-carrying fertilizers are especially desirable 
for improving color. That this last idea is erroneous is shown by the 
results of many carefully conducted investigations of recent years, in- 
vestigations that are reported in more detail later in this section. The 
data in this chapter afford some idea of the approximate amounts of 
potash that are required for usual tree growth and production. Though 
these are considerable in comparison with the amounts required by 
many farm crops, the enormous quantities of this element found within 
reach of tree roots in most soils make the application of potash-carrying 
fertilizers seem of doubtful promise, at least so far as supplying the plant 
with larger quantities of this element is concerned. This statement is 
supported by numerous experiments in which potash in different forms 
has been applied to orchard trees apparently without positive results, 
and also by soil investigations like those of Hopkins and Aumer, 101 
showing that in 6 feet of soil covering an area of 1 square mile of the 
Illinois corn belt there is as much potash as is applied annually in fertil- 
izers to all the farms of the United States. It is true that many orchard 
soils are not so liberally supplied with potash as those of the Illinois corn 
belt; nevertheless, so far as data are available, they indicate the presence 
of quantities much in excess of probable requirements for many years, 
if not for many generations. Beneficial results in greater vegetative 
growth and increased yields have been reported occasionally from the 
application of potash-carrying fertilizers to orchard soils. The question 

10 



146 



FUNDAMENTALS OF FRUIT PRODUCTION 



may be raised, whether this increase in growth or yield is not due to 
indirect effects of the potash on some other factor, such as the availa- 
bility of phosphorus, or to the influence of other elements with which 
potassium is combined in the fertilizer. This last suggestion receives 
some support from the fact that in most cases when the muriate and 
sulfate of potash have been used side by side, the sulfate has almost 
invariably given a much more pronounced response than the muriate and 
has often yielded positive results when the muriate has given entirely 
negative results. 

Seasonal Distribution of Potassium.— Rather marked differences between 
potassium and the elements already considered, in translocation, storage and 
utilization are shown by the seasonal changes in its distribution within the plant. 

In Leaves. — Fruit buds are much richer than leaf buds in potassium con- 
trasting with the condition presented by phosphorus. 

The potash content of fruit buds has been found to be 2.290 per cent, of the 
dry weight in the cherry and 2.344 per cent, in the plum, while that of leaf buds 
was 1.961 per cent, in the cherry and 2.213 per cent, in the plum. 155 

The variation in the percentage content of potash in leaves during the growing 
season is illustrated by the figures in Table 33. As with phosphorus and nitrogen 
the percentage of potassium decreases as the leaf grows older and the absolute 
amount present in the leaf passes through a maximum, as Table 34 shows. 





Table 
(Ir 


33. — Potash Content of Leaves 
i percentage of dry weight ]f5 ) 






Apple 


Pear 


Cherry 


May 9 

May 14 

June 22 


3.150 

1.886 
1.927 

1.601 


2.460 

1.690 
1.770 
1.320 


3.006 

2 782 


Aug. 29 

Oct. 2 

Oct. 15 


2.637 
3.080 



However, the decrease in the potash content of leaves during the fall is slight 
in all fruits for which data are available and there is no decrease in the pear. The 



Table 34. — Grams 


of Potash 


in 100 Leaves 155 






Apple 


Pear 


Cherry 


Plum 


July 14 


0.603 
0.625 
0.702 
0.622 

0.495 


0.300 
0.304 
0.298 
0.305 

0.324 


0.603 
0.590 
0.603 
0.572 
0.524 
0.376 


0.832 


July 31 


0.772 


Aug. 18, 21 


0.766 


Sept. 3, 4, 6 


0.762 


Oct. 7 




Oct. 23, 27, 29 


0.616 


Nov. 4 









INDIVIDUAL ELEMENTS 147 

marked difference in this respect between potassium and phosphorus or nitrogen 
suggests a corresponding difference in their utilization by the plant. Possibly 
the elaboration of potassium is not localized in the leaf. 

Though the amounts of potassium removed from the leaves before they fall 
seem small in comparison with phosphorus, there is none the less evidence of 
potassium storage in the branches. Table 35 gives data showing the withdrawal 
of potash from the leaves into the branches. 

Table 35. — Grams of Potash in 100 Branches of the Horse-chestnut and 

Their Leaves 5 





Branches 


Leaves 


July 29 


1.763 
2.249 
2.575 
2.671 


18.876 


Sept. 11 


14.236 


Oct. 14 

Nov. 16 


13 . 400 



In Branches, Roots and Trunks. — The leaves lose more potassium than can be 
accounted for by the gain in the branches on which they were borne, indicating 
that considerable amounts of potash are washed from the leaves by rain. The 
relative amounts of potash in the ash of sap-wood and bark resemble those of 
phosphorus. In one series of determinations the ash of the sap-wood of the pear 
was 22.25 per cent, potash, of the bark 6.2 per cent.; the sap-wood ash of the 
apple was 16.19 per cent, potash, the bark ash 4.93 per cent, and the sap-wood 
ash of the grape was 20.84 per cent, potash, the bark ash 1.77 per cent. 64 In 
the sap-wood ash there is more potash than any other element except calcium ; in 
the bark the potash content is lower and the calcium content higher, but the 
absolute amount in the bark is probably greater than in the sap-wood on account 
of the bark's higher ash content, as has been pointed out in the discussion of 
phosphorus. 

Table 36, showing seasonal variations in the potash content of the root, trunk 
and branches of a 7-year old apple tree, gives additional evidence of the storage 
of potassium in the branches. 

Apparently potassium is stored in old branches to a relatively greater extent 
than nitrogen or phosphorus, for in the 3-, 4- and 5-year old branches the potash 
content reaches a minimum in May though the 1- and 2-year old branches have a 
high content at that time and do not reach a minimum until later. The young 
roots and branches are richer in potassium, as in phosphorus and nitrogen, than 
the older parts of the tree. 

Potassium probably is stored in both bark and sap-Avood. The layers of 
bark nearest the cambium are richest in this element. Furthermore, the young 
bark of the oak, horse-chestnut and walnut contains more potash in percentage 
of total ash at the time of greatest vegetative activity in the spring than later in 
the season. 52 Similar seasonal differences occur in the potash content of the sap- 
wood of these trees, while the heart- wood not only contains considerably less but 
its content is subject to much smaller fluctuations. 17 Weber 197 found that in 
beeches producing many seeds, the sap-wood was particularly rich in potash 



148 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 36. — The Potash Content of a 7-year Old Apple Tree 
(Expressed in percentages of dry weight 23 ) 





Dormant, 


Buds 


In bloom, 


Growth 


Leaves 




Dec. 3 


swelling, 
Apr. 20 


May 18 


over, 
July 12 


falling, 
Oct. 12 


Summer's growth 








1.03 


0.60 


1-year old branches 


0.46 


0.49 


0.62 


0.52 


0.47 


2-year old branches 


0.33 


0.33 


0.39 


0.33 


0.40 


3-year old branches 


0.30 


0.27 


0.28 


0.31 


0.33 


4-year old branches 


0.24 


0.25 


0.20 


0.25 


0.29 


5-year old branches 


0.20 


0.22 


0.17 


0.20 


0.28 


Trunk 


0.15 


0.21 


0.20 


0.18 


0.25 


Large roots 


0.42 


0.40 


0.39 


0.43 


0.40 




0.57 


0.45 


0.45 


0.54 


65 







while the phosphorus content was not materially greater than in trees bearing 
few seeds. Warren 194 found that in peach, apple, plum and pear trees the ash of 
the leaves contained less potash in years when the crop was large (see Table 37). 

Table 37. — The Potash Content of Peach Leaves in Bearing and Non-bearing 

Years 194 



In percentages of 
dry matter 



In percentages of 
total ash 



First four years . . . 
Five bearing years 
1904 (no crop) 



2.12 
1.42 
1.80 



17.7 
11.2 
15.8 



This suggests that fruit trees usually take up more potassium from the soil than 
is actually required, when they are not bearing fruit. 




Fig. 16.- — Potassium content of apple spurs in percentages of dry weight; bearing 
spurs represented by continuous lines, non-bearing spurs by broken lines and barren spurs 
by dot-dash lines. (After Hooker. 100 ) 

In Spurs. — Figure 16 shows that the potassium content of bearing spurs rises 
to a very high maximum in May. This increment pusses into the fruit and the 



INDIVIDUAL ELEMENTS 



149 



potassium content of the spur falls to a minimum in September. The low figure 
for barren spurs throughout the year is noteworthy, as is also the increase in the 
potassium content of spurs in the off year at the time when fruit buds are being 
differentiated (June). 

In Fruit. — The data in Table 38 illustrate the increase in potash content 
accompanying fruit development. 

Table 38. — Grams of Potash in 1,000 Berries of the Grape 138 

July 27 1.875 Sept. 17 4.824 

Aug. 9 2.306 Sept. 28 5.588 

Aug. 17 2.490 Oct. 5 6.179 

Aug. 28 (softening) 2 . 194 Oct. 12 (fully ripe) 4 . 924 

Sept. 7 4.288 Oct. 22 (rotted) 4.317 

The leaves, fruit and seeds are the parts richest in potassium (see Table 40). 
In most edible fruits potash comprises 30 to 60 per cent, of the total ash and the 
absolute amounts shown in Table 39 are very considerable. 

Table 39. — Pounds of Potash in 1,000 Pounds of Fresh Fruit 29 

Almonds 9 . 95 

Apricots 3 . 01 

Apples 1 . 40 

Bananas 6 . 80 

Cherries 2.77 

Chestnuts 3. 67 

Figs 4.69 

Grapes 2. 55 



Lemons 2 . 54 

Olives 9.11 

Oranges 2.11 

Peaches 3 . 94 

Pears 1 . 34 

French prunes 3 . 10 

Plums 3.41 

Walnuts 8.18 



The potash content of seeds is about the same as that of fruits, being usually 
20 to 50 or even 60 per cent, of the total ash. 41 

Table 40. — Potash Content of Apple Trees of Various Ages 

(1 to 9 from Thompson,™ 13 and 100 from Roberts,™ 30 from Van Slyke 190 ) 

A Percentage of dry weight. B Grams 



Age 


Leaves 


New growth 


Trunk and 
branches 


Roots 


Fruit 


A 


B 


A 


B 


A 


B 


A 


B 


A 


B 


1 


1.25 


0.33 






0.21 


0.20 


0.30 


0.18 






2 


1.22 


0.88 






0.34 


0.81 


0.55 


0.71 








3 


1.35 


1.22 






0.30 


2.31 


0.53 


2.39 








4 


1.13 


1.53 






0.31 


4.37 


0.48 


2.43 








5 


1.65 


7.79 


0.72 


1.56 


0.47 


16.84 


0.57 


9.34 








6 


1.00 


6.04 


0.61 


1.56 


0.35 


14.87 


0.50 


16.30 








7 


1.24 


11.64 


0.55 


2.40 


0.36 


24.45 


0.46 


18.70 


1.12 


13 


87 


8 


1.42 


33.50 


0.64 


4.17 


0.31 


39.00 


0.48 


36.95 


1.20 


16 


56 


9 


2.08 


75.20 


0.61 


6.76 


0.33 


80.60 


0.49 


68.40 


1.17 


39 


83 


13 


1.76 


127.00 




















30 


0.59 


122 . 00 


0.60 


9.00 










0.70 


589 


00 


100 


1.43 


598. 00 


0.80 


4.00 


0.41 


2697 . 00 


0.22 


417.00 


.... 







150 



FUNDAMENTALS OF FRUIT PRODUCTION 



In Various Tissues of Trees of Different Age. — Table 40 shows the variations 
with age in the several parts of apple trees. It is noteworthy in connection 
with what has been said of the relations of potash content to bearing that the 
30-year old trees have the lowest percentage of potash in the leaves. These trees 
were in full bearing as reference to the last column of the table shows. Further- 
more, there is no reduction in the percentage of potash in the leaves of the 100- 
year old tree which had ceased bearing. 

The leaves of a tree in full bearing contain much less potassium when they 
fall than its fruit. This is true of potassium even to a greater degree than of 
phosphorus, as Table 41 shows. 

Table 41. — Pounds op Potash in Parts op a Full Grown Tree 190 



Apple 



Peach 



Pear 



Plum 



Fruit or fruit pulp 

Stones 

Stems 

Leaves 

New growth 



1.28 



0.27 
0.02 



0.29 
0.01 

0.27 
0.03 



0.16 



0.09 
0.02 



0.14 
0.01 
0.01 
0.15 

0.01 



0.19 



0.04 
0.01 



SULPHUR 

Data are not available to present a picture of what happens to sulphur 
in the fruit tree as has been attempted with nitrogen, phosphorus and 
potash. The inorganic sulphate taken from the soil is incorporated into 
organic compounds as both sulphate and sulphide sulphur. As sulphate, 
it occurs in some of the mustard oils, such as sinigrin; as sulphide, it 
occurs in cystin, one of the amino-acids used in the construction of most 
proteins. 

Because considerable amounts of sulphur are lost in ashing, deter- 
minations of the sulphur content of ash are of little value. There are 
indications that plants contain as much or more sulphur than phosphorus, 
but satisfactory analyses are yet to be made. 

The data in Table 42 are representative of a few reliable analyses of 
sulphur in fruit plants. They show that fruit contains approximately as 
much sulphur as phosphorus. 

Table 42. — Pounds of Sulphur in 1,000 Pounds of Fresh Fruits 166 



Apples 0.43 

Raspberries . 35 

Gooseberries 0.12 

Dewberries . 37 

Cherries 108 

Red currants . 56 

Blackberries . 40 



Grapefruit 0.20 

Peach pulp 0.14 

Oranges . 26 

Lemons . 22 

Limes . 47 

Pineapple 0.39 



Sulphur has been thought generally to be present in most soils in 
amounts sufficient to meet the requirements of crop plants and recent 



INDIVIDUAL ELEMENTS 151 

investigations would indicate that this condition holds for a great many 
soils. Thus the sulphur content of Illinois soils has been reported as 
ranging from 280 to 750 pounds per acre in the top 6% inches. 179 Since 
the average growing crop removes only 4 to 10 pounds of this element per 
acre and losses through seepage are likely to be nearly offset by additions 
through rainfall, it would appear that the application of sulphur as fer- 
tilizer to such soils does not offer much promise of increased crop returns. 
However alfalfa removes 40 pounds per acre per year and cabbage nearly 
as much. Moreover there are many soils not so well supplied with 
sulphur and Shull 168 is authority for the statement that "the normal 
sulphur content of soils is sufficient for from 15 to 70 crops, provided 
there are no additions from outside sources as from rainfall. Even if we 
count in the rainfall sulphur, it is probable that sulphur is just as often a 
limiting factor as is phosphorus, or nitrogen, or potassium." The soils 
poor in sulphur and applications of compounds containing this element 
of the Rogue River valley in southern Oregon have been found very 
have greatly increased yields of leguminous crops. 153 In some instances 
these increases have amounted to 500 to 1,000 per cent. Without doubt 
these conditions are very exceptional; nevertheless the results suggest 
that sulphur may be a much more important limiting factor in soil pro- 
ductivity than has been considered generally. Recent investigations 
indicate that sulphates have a special influence on root development. 86 
This is particularly marked with red clover and rape, where sulphate 
applications resulted in root elongation and consequently in an extension 
of the feeding area and a greater ability to withstand drought. Little is 
known regarding the direct effect of sulphur-carrying fertilizers on 
deciduous fruits. However, the application of 178 pounds of sulphur per 
acre to certain vineyard soils has resulted in increases in yield of 19.2 to 
32.7 per cent, and in increases of 25.03 to 27.3 per cent, when applied with 
14 tons of stable manure. 28 Though no direct influence of sulphur- 
carrying fertilizers upon tree growth or production was reported in the 
Rogue River valley experiments the crops so greatly benefited by their 
application were those commonly grown as intercrops and cover crops in 
the orchard. Through them the trees might be greatly benefited in 
later years. 

These facts taken with the lack of data on the distribution of sulphur 
in plants accentuate the importance of more analytical and experimental 
work on this element. Sulphur has been neglected because it was 
thought to occur in relatively small amounts, but the small amounts 
found were due to faulty methods of analysis and sulphur is just as 
essential to plants and as worthy of consideration as phosphorus. 

IRON 

Iron occurs in plants in even smaller amounts than sulphur. It is 
found in organic combination in some nucleic acids. 148 



152 FUNDAMENTALS OF FRUIT PRODUCTION 

Iron usually constitutes 1 to 4 per cent, of the leaf ash. Grape leaves have 
been known to have an exceptionally high figure, 10.20 per cent. 57 The absolute 
iron content of leaves increases with age, though the percentage composition of 
the leaf remains fairly constant. 

Table 43. — Iron Oxide Content of Beech Leaves 145 
(In percentage of total ash) 

May 16 0.8 

July 18 1.4 

Oct. 15 1.3 

The ash of bark ranges from 0.2 to 3 per cent, of iron, the amount often 
increasing with age; for example 0.2 per cent, has been found in the apple and 
2.545 per cent, in the grape. 64 Wood ash has but little iron, usually from 0.1 to 
0.8 per cent. — 0.16 per cent, in the pear, 0.42 per cent, in the apple and 0.635 per 
cent, in the grape. 64 Exceptionally high figures have been found in the olive, 
2.11 per cent, of the ash, and in the orange, 3.08 per cent. 50 

Table 44. — The Iron Oxide Content of Fruits 59 and Seeds 43 

(In percentages of total ash) 

Fruits Seeds 

Banana 1.46 Grape 0.37 

Plum 2 . 54 Almond . 55 

Apple 1.40 Walnut 1.32 

Pear 1.04 Coffee 0.65 

Orange 0.46 Chestnut 0.14 

Grape 1.04 

Olive 0.72 

Iron is a constituent of practically all soils; furthermore it is always 
found in quantities sufficient for the requirements of crop plants. How- 
ever, in many cases it is held in the soil in a form unavailable to the plant; 
consequently the plants may suffer because of iron starvation. Refer- 
ence has been made to this in connection with the discussion of soil 
reaction and more is said regarding the disturbances caused by a lack of 
iron under the heading of Surpluses and Deficiencies. 

MAGNESIUM 

The most important organic compound containing magnesium is 
chlorophyll. This element also occurs in organic combination in salts of 
arabic acid and in the globoid of aleurone grains. Some proteins are 
thought to contain magnesium. Anthocyan pigments are complex 
compounds with salts of magnesium, calcium or other metals. 167 

The absolute amount of magnesia in leaves increases as they grow 
older. Thus 500 leaves of Platanus were found to contain 0.24 gram 
of magnesia on June 13, 0.85 gram at the end of August and 0.69 gram 
at leaf fall, showing a slight decline. 66 However, there is not much change 
in the percentage of magnesia in the total ash. On May 16, in beech 



INDIVIDUAL ELEMENTS 



153 



leaves it was found to be 4.36 per cent.; on July 18, 5.63 per cent, and 
on Oct. 15, 4.12 per cent. 145 The magnesium, like the iron content, keeps 
pace with leaf development; this increase may be associated with the 
chlorophyll content of the leaf. However, there is some evidence that 
magnesium is withdrawn to' the branches from the leaves late in the 
season. There are also indications of magnesium storage in the sap- 
wood, which is slightly richer in magnesium than the heart-wood. Dur- 
ing the spring, there is more magnesium in the sap-wood than at other 
times. Weber found that in beeches producing many seeds, the sap-wood 
was especially rich in magnesia and potash, as compared with trees 
bearing few seeds. 197 The sap-wood ash of the pear has been found to 
contain 3 per cent, magnesia, of the grape 4.4 per cent, and of the apple 
8.49 per cent. 64 

The magnesia content of bark ash decreases with age. In young 
bark it is 3 to 8 per cent., as in the leaves; in old bark 2 to 5 per cent. 
Thus the magnesia of pear bark has been found to be 9.4 per cent, of the 
ash, while in the apple bark it is 1.5 per cent, and in grape bark 0.8 
per cent. 64 The sieve tubes sometimes contain magnesium phosphate; 
this may be a form of storage. 

As a rule fat-storing seeds are richer in magnesia than starchy or reserve- 
cellulose seeds; in the almond, magnesia has been found to be 17.66 per cent, of 
the ash, in the walnut 13.03 per cent., while in coffee (Coffea arabica) beans it is 
9.69 per cent, and in chestnuts 7.47 per cent. 42 

Table 45 shows that the leaves of fruit trees contain much more magnesium 
than the fruit. In the apple the magnesia content of the fruit has been found to 
be 0.10 per cent, of the dry weight; of the leaves 1.03 per cent, and of the new 
growth 0.30 per cent. 190 

Table 45. — Pounds of Magnesia in Parts op a Mature Tree 190 





Apple 


Peach 


Pear 


Plum 


Quince 


Fruit or pulp 

Stones 

Stems 

Leaves 

New growth 


0.18 

0.47 
0.01 


0.02 
0.01 

0.24 
0.02 


0.02 

0.06 
0.01 


0.02 

0.01 
0.07 
0.01 


0.02 

0.05 
0.01 



Table 46. — The Magnesia Content of Fruits 59 
(In percentages of total ash) 

Pineapple 9 . 79 Pear 

Banana 9.21 

Strawberry 2.93 

Plum 4 . 69 

Apple 8.75 



5.22 

Orange 8 . 06 

Grape 2.61 

Olive 0.18 



154 



FUNDAMENTALS OF FRUIT PRODUCTION 



Though magnesium is necessary for plant growth, it is not required 
in large quantities and so far as is known all soils contain sufficient amounts. 
Certainly no data are available showing the necessity of fertilizing fruit 
plantations with magnesium-carrying compounds. 



CALCIUM 

Calcium is for the most part absent from the growing points and from 
embryonic tissues generally and it accumulates in all tissues with age. 
This indicates that calcium is utilized in ways very different from the 
other essential elements, a surmise substantiated by the fact that it is not 
necessary for the growth of fungi. 

It is found organically combined in calcium oxalate crystals, in 
calcium pectate of the middle lamella which holds adjoining cells together, 
in salts of arabic acid, in the globoid of aleurone grains and in the antho- 
cyan pigments. It is prevalent also as calcium carbonate. 

Seasonal Distribution of Calcium. — Calcium differs from the elements 
previously discussed in its seasonal history in the tree. It has been 
mentioned that where potassium is present in large amounts, calcium 
is usually present in small amounts and vice versa. 



In Buds and Leaves. — The calcium content of buds is not great as compared 
with that of other plant tissues. Leaf buds have more lime, but less potassium, 
than fruit buds. In percentages of dry weight, the lime content of leaf buds has 
been found to be 1.364 per cent, in the cherry and 2.365 per cent, in the plum; 
that of fruit buds was 1.113 per cent, in the cherry and 1.761 per cent, in the 
plum. 155 Very heavy deposits of calcium oxalate have been found in resting 
fruit buds, the amount decreasing after growth .begins. As leaves grow older 
their percentage lime content increases, as Table 47 shows. The absolute lime 
content increases also (c/. Table 48), 



Table 47. — Lime Content of Leaves 165 
(In percentage of dry weight) 



Apple 



May 9. 
May 14 
May 18. 
June 22 . 
Aug. 29. 
Sept. 30 
Oct. 2.. 
Oct. 15. 



1.186 



2.166 
2.762 

3 . 723 



Pear 



0.754 



1.977 
3.147 
3.473 



Cherry 



1.511 

2.699 
3.987 

4.55S 



Plum 



1.025 
3.512 
4.591 
5.696 



INDIVIDUAL ELEMENTS 
Table 48. — Grams of Lime in 100 Leaves 155 



155 



Apple 



Pear 



Cherry 



Plum 



July 14 

July 31 

Aug. 18, 21... 
Sept. 3, 4, 6 . . 

Oct. 7 

Oct. 23, 27, 29 
Nov. 4 



0.894 
0.966 
1.191 
1.010 



0.793 



0.396 
0.445 
0.475 
0.515 

0.335 



0.727 
0.791 
0.892 
0.939 
1.100 
0.765 



0.738 
0.697 
0.699 
0.758 

0.978 



In most cases there is a reduction in the absolute calcium content before leaf fall, 
probably because of the dissolving action of rain. The lime content of full 
grown leaves is often very great, sometimes constituting 52.82 per cent, of the 
ash of the olive, 54.33 per cent, of the ash of the apple, 56.83 per cent, of the ash 
of the orange and 34 to 60.9 per cent, of the ash of the grape. 54 

The data in Table 49 showing the simultaneous changes in the calcium 
content of leaves and branches indicate that there is no removal of calcium from 
the leaves to the branches. 



Table 49. — Grams of Lime in 100 Branches of Horse-chestnut and Their 

Leaves 5 



Branches 



Leaves 



July 29 . 
Sept. 11 
Oct. 14. 
Nov. 16 



4.274 
6.549 
5.938 
5.804 



27.292 
39.785 
51.201 



In Bark and Wood. — Young bark contains considerable lime, about 40 per 
cent, of the ash, chiefly in the form of calcium carbonate. It increases with age to 
70 or 80 per cent, of the ash, sometimes reaching 95 per cent, in oak bark. 55 
Pear bark ash has been found to contain 33.88 per cent, lime, apple bark ash 
51.84 per cent, and grape bark ash 42.05 per cent. 64 The seasonal variation is 
counter to that of potassium, there being proportionately less calcium in the 
bark in the spring than at other times. For example, in the walnut, bark ash was 
found to contain 8.37 per cent, calcium on May 31 and 70.08 per cent, on Aug. 
27. 5S Calcium increases with age in the wood also and the heart-wood contains 
progressively more than the sap-wood, as Table 50 shows. 

In general 60 to 78 per cent, of wood ash is lime. In the orange it has been 
known to rise to 68.88 per cent. 49 In the sap-wood there is less; in the pear 
there has been found 27.39 per cent., in the apple 18.65 per cent, and in the grape 
25.67 per cent. 64 In the heart- wood, the vessels and sometimes the tracheids, 
wood fibers and parenchyma cells are filled with spherites of calcium carbonate. 
The older the wood, the more calcium there is in its ash. 



156 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 50. — Ash Content of Heart-wood in a Red Beech 209 
(In percentages of dry weight) 






Rings 


Ash 


CaCOs 


1 to 15 


1.162 


0.579 


15 to 25 


0.825 


0.251 


25 to 35 


0.645 


Trace 


35 to 45 


0.612 


Trace 


45 to 60 


0.555 




60 to 83 


0.458 




83 to 94 (sap-wood) 


0.205 





In Fruits. — In fruit trees, the calcium required by the crop is insignificant 
compared with that lost with the leaves and sometimes it is less than that in 
the new growth. This is shown in Table 51. In one set of determinations the 



Table 51. — Pounds op Lime 


in Parts 


of a Full 


Grown Tree 190 




Apple 


Peach 


Pear 


Plum 


Quince 


Fruit or fruit pulp 

Stones 

Stems 


0.12 

1.42 
0.08 


0.02 
0.00 

0.79 
0.14 


0.03 

0.25 
0.04 


0.01 
0.00 
0.02 
0.22 
0.09 


0.01 


Leaves 

New growth 


0.19 
0.07 



lime in apple leaves was 3.10 per cent, of their dry weight; in new growth 2.39 
per cent, and in the fruit 0.06 per cent. 190 However, the lime content of fruits 
is not inconsiderable (see Table 52). 



Table 52. — Pounds of Lime in 1,000 Pounds of Fresh Fruit 5 



Almonds . 



1 . 04 Lemons 1 . 55 



Apricots 0.16 

Apples 0.11 

Bananas 0.10 

Cherries . 20 

Chestnuts 1 . 20 

Figs . 85 

Grapes . 25 



Olives 2 . 43 

Oranges . 97 

Peaches 0.14 

Pears 0.19 

French prunes . 22 

Plums 0.25 

Walnuts 1 . 55 



According to Trabut, "a high lime content is a very favorable factor in grow- 
ing olives for oil production, as olives produced in limestone regions are richer in 
oil and the oil is of better quality than where the soils are deficient in 
this component." 105 

The Demand and the Supply. — In general it may be said that the 
calcium requirements of fruit trees are insignificant compared with the 
amounts usually available in the soil. For instance, it has been shown 
that certain typical Illinois soils contain quantities sufficient in the sur- 



INDIVIDUAL ELEMENTS 157 

face layers to produce 5,000 to 55,000 heavy corn crops if the supply is not 
replenished and if it becomes available gradually. 180 All the chemical 
analyses of fruit soils given in the chapter on Orchard Soils indicate that 
the danger from calcium starvation in the orchard is very remote. In 
all probability the amounts of calcium found in plant tissues are often 
much in excess of their nutritive requirements. There is no doubt that 
calcium is of use in the elimination of poisonous products of catabolism, 
such as oxalic acid, but it seems not at all unlikely that in many cases the 
oxalic acid is produced as a means of rendering a surplus of calcium 
insoluble. 

Many orchard fertilizer experiments have been conducted in which 
lime has been used, either alone or in combination. The results attending 
these experiments have been variable, but on the whole negative in 
character. Certainly there is no clear evidence available to show that 
liming the soil is of any direct benefit to the trees. It has been pointed 
out that applications of lime may aid nitrification in the soil and may be 
of use to other cultures that are being grown in the fruit plantation and 
thus indirectly to the trees; on the other hand, it has been shown also 
that they may have a very deleterious influence on tree or vine growth and 
these deleterious influences are of sufficiently frequent occurrence in 
actual field practice to suggest caution. It may be recalled that the 
purpose for which lime is generally used with field crops, namely the 
correction of soil acidity, needs but little consideration in deciduous fruit 
production. 

OTHER MINERAL ELEMENTS 

Beside the elements already discussed, there are others that are of 
universal occurrence in plants, though they are generally considered to be 
unessential. However, copper which occurs in very small amounts 
in plant tissues is considered by Maquenne and Demoussey 129 to be an 
essential element. 

Silicon. — Silica is universally present, though the amount is very variable. 
In leaves, for example, it may be present in mere traces or it may constitute 80 
per cent, of the ash. In grape leaves amounts ranging from 1.61 per cent, to 
39.44 per cent, have been found, the amount usually increasing with age. 58 
Table 53 illustrates this point. 

Table 53. — Grams of Silica in 100 Branches of Horse-chestnut and Their 

Leaves 5 





Branches 


Leaves 


July 29 

Sept. 11 

Oct. 14 

Nov. 16 


0.095 
0.165 
0.084 
0.056 


14.187 
18.812 
18.195 



158 



FUNDAMENTALS OF FRUIT PRODUCTION 



Bark ash usually contains less than 2 per cent, of silica; for example, 0.4 per 
cent, in the pear and 0.6 per cent, in the apple. 64 The ash of grape bark has been 
shown to contain 14.3 per cent, silica. 64 Wood ash usually contains less than 
3 per cent, of silica; for example, 0.3 per cent, has been recorded for pear wood, 
1.65 per cent, for apple wood and 2.8 per cent, for grape wood. 64 The ash 
of olive wood has been found to contain as much as 14.23 per cent, silica. 51 As a 
rule the heart-wood contains a higher percentage than the sap-wood. 

Fruits contain silica in amounts shown in Table 54. The seed usually con- 
tains less, as the same table shows, though a trace at least is always present. 



Table 54.- 



■ 9 and Seeds 43 



Seeds 

Chestnut 1 

Grape 1 

Coffee 

Cocoanut 



54 
04 
54 
50 



Walnut Trace 



-The Siuca Content of Fruits 
(In percentages of total ash) 
Fruits 

Pineapple 5 . 77 

Banana 5.93 

Fig 2.34 

Plum 3.15 

Apple 4.32 

Pear 1.49 

Orange . 44 

Grape 1.00 

Olive 0.65 

Silicon usually is associated with the cell wall and sometimes confers strength 
and stability on a plant tissue. However, the strongest and hardest of plant 
materials are often of very nearly pure cellulose ; hence, a lack of silicon does not 
necessarily involve mechanical weakness of mature tissues. 

Sodium. — Sodium also is of universal occurrence in plant tissues. Leaves 
usually contain 1 to 3 per cent. Table 55 indicates the seasonal variation in 
absolute amounts in five hundred Platanus leaves. 

Table 55. — The Seasonal Variation in Soda Content of Platanus Leaves 53 

(Grams in 500 leaves) 

June 13 0.3152 Oct. 8 0.2898 

May 15 0.4187 Oct. 24 0.2439 

Aug. 22 0.4299 Nov. 5 0.2273 

Sept. 7 :... 0.5641 

Bark and wood ash usually contain but little soda, 3.495 per cent, having been 
recorded in the ash of apple bark and 0.27 per cent, in that of grape bark. 64 The 
wood of the sweet cherry has been known to contain as much as 10.13 per cent. 48 
As a rule there is less soda in the ash of heart-wood than in that of sap-wood, 
certain sap-wood records showing for the pear 1.84 per cent, soda; for the apple, 
3.275 per cent, and for the grape, 2.06 per cent. 64 Fruits contain soda in the 
widely varying amounts shown in Table 56. 

Table 56. — The Soda Content of Fruits 59 
(In percentages of total ash) 

Pineapple 6.75 Apple 26.09 

Banana 26.27 Pear 8.52 

Fig 19.63 Orange 13.47 

Plum 9.05 Olive 7.53 



INDIVIDUAL ELEMENTS 159 

Seeds usually contain less than fruits, from 1 to 2 per cent., but walnuts have 
been recorded as having 2.25 per cent., cocoanuts 8.39 per cent, and dates 9.03 
per cent. 41 

Though sodium is regarded as unessential for the growth of very many 
plants, investigations with turnips, radishes, beets, cucumbers, buckwheat, 
oats, potatoes and a number of other crop plants, indicate that this 
element can partially replace potassium when the latter is not present in 
amounts sufficient for good growth. 88 "In the field, however, more 
potassium was removed in the larger crops which usually resulted when 
sodium was increased in connection with an insufficient amount of 
potassium, and this was in spite of the fact that sodium frequently de- 
creased the percentage of potassium in the crop. A portion of the bene- 
fits arising from the use of sodium in the field is, therefore, attributable to 
indirect action, but the solution work indicates that also direct beneficial 
effects were probably obtained in the field." 88 

Probably this function of sodium is of little direct importance in the 
deciduous fruit plantation, since it is very seldom that a lack of potassium 
is a limiting factor; however, it is at least a matter of interest. 

Chlorine. — Chlorine occurs in many plants, but seldom in large amounts except 
in salt marsh plants. In leaves the amount varies from 25 per cent, of the total 
ash to mere traces. The chlorine content of bark ash is low, certain records in 
the pear showing 1.7 per cent., in the apple 0.33 per cent, and in the grape 0.4 
per cent. 64 The chlorine content of wood ash is even less, being 0.31 per cent, in 
the pear, 0.255 per cent, in the apple and 0.02 per cent, in the grape. 64 The 
chlorine content of fruits is more variable, but never very great. 

Table 57. — The Chlorine Content of Fruits 59 
(In percentages of total ash) 

Pineapple Trace Plum . 38 

Banana 2 . 69 Orange 2 . 35 

Fig 0.83 Olive 0.16 

Seeds usually have 0.5 to 1.5 per cent, of chlorine in the ash, but the amount 
present varies greatly. Walnuts and almonds have mere traces. Other records 
are: for chestnuts, 0.52 per cent, of the ash, for grape seeds, 0.27 per cent, and for 
the cocoanut, which grows on the sea-shore, 13.42 per cent. 44 

There is no definite relation between the amount of sodium and the amount 
of chlorine a tissue contains. 

It would appear from the preceding statements that no benefit would 
be derived from the chlorine in fertilizers carrying this element. Com- 
mon salt has often been suggested as having possible value as a fertilizer 
and has been tried in a limited way. So far as records are available they 
indicate that it is of no value for deciduous or for most other fruit trees. 
However, greatly increased yields of the mango have been reported in the 
province of Bombay, India, from applying 10 pounds to the tree and 



160 FUNDAMENTALS OF FRUIT PRODUCTION 

likewise marked increases in yield from its application to cocoanuts. 78 
To what extent these increases were due to direct or indirect effects of the 
sodium or the direct or indirect effects of the chlorine is not known. 

Aluminum and Manganese. — Manganese is a common constituent of the 
bark, where it seldom exceeds 1 per cent, of the ash. The other parts of the 
tree usually have less than the bark. Aluminum and manganese combined 
average 0.5 to 0.9 per cent, of wood ash. Aluminum is not uncommon in seeds. 
It sometimes comprises 0.062 per cent, of the ash of fig seeds and 0.138 per cent, 
of the ash of almonds. 45 Aluminum is capable of forming complex salts with 
the anthocyan pigments. 67 The color of the pigment depends on the base which 
it contains, which accounts for the fact that the hydrangea (H. hortensis) develops 
blue instead of pink flowers when soluble aluminum compounds are applied to 
the soil in which it grows. 135 

Summary. — Certain elements, especially nitrogen, phosphorus, potas- 
sium and sulphur are present in greatest amount in young tissues. Cer- 
tain amounts are stored in the bark over the winter and in the spring a 
supply is on hand for the rapid development of leaves and shoots, flowers, 
fruit and seeds. Since the seeds themselves are storage organs and in addi- 
tion contain embryonic tissue, they accumulate these elements in relatively 
large proportions. Magnesium and iron likewise are stored in the bark 
and in the wood as well. They are utilized in new growth, though they 
appear to be more equally distributed in mature and in embryonic 
tissues. All of these elements show more or less mobility and are trans- 
located to regions where they are more in demand. The plant con- 
serves its supply and withdraws at least a part of the amount contained 
in the leaves, after they have ceased to function. 

Calcium and silicon are very nearly absent from embryonic tissues. 
They accumulate throughout the plant with age. There are no indica- 
tions that these elements are stored for future use and to a great degree 
they remain where they are deposited. 

With respect to the other mineral elements found in plants, little 
can be said in generalization. This is because no regularity has been 
observed in the amounts present or in their seasonal variation. 



CHAPTER IX 

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 

The essential elements discussed in the previous section are used 
ultimately in the construction of the plant's substance. They are indis- 
pensible because the plant cannot be constructed unless each one of 
them is present. 

ASSIMILATION AND LIMITING FACTORS DEFINED 

The term assimilation, in its broadest sense, is used to describe the 
process by which a plant builds up the substances that comprise it out of 
compounds obtained from its environment. To be sure any compound 
will not serve; certain specific materials are necessary. Assimilation 
depends on a supply of such materials and on a source of energy. The 
amount of assimilation and hence of growth is determined by the opera- 
tion of the principle of limiting factors. 

Most plants require at least seven elements in combined form from 
the soil, namely, S, P, N, K, Fe, Mg and Ca. If «S, /8P, 7 N, 5K, 
eFe, f Mg and rjCa combine exactly to produce a unit amount of growth 
in some particular plant, say an apple tree, and if aS, bP, cN, dK, eFe, 
/Mg and gCa are present in a particular soil in available form, the maxi- 
mum amount of apple tree tissue that can be grown in that soil will be 
the smallest of the fractions a/a, b/fi, c/y, d/8, e/e, //f, g/rj. That 
element which gives the smallest fraction is the limiting factor of growth." 

The principle of limiting factors applies not merely to nitrogen and the 
essential mineral elements, but also to water, to carbon dioxide and to 
oxygen which likewise are essential nutrients entering into the composi- 
tion of the plant. Moreover the principle covers the effects of external 
factors such as temperature and light which also may be limiting factors 
of assimilation. All of these possible limiting factors of assimilation 
and growth constitute the external stimuli to which the organism reacts 
and these reactions tend to overcome the limiting factors of assimilation 
and so bring the organism in the most favorable situation for assimila- 
tion that circumstances permit. In consequence of the reactivity of 
the plant and its apparent complete adjustment to its environment 
the principle of limiting factors sometimes may seem not to be operative. 
This, however, is not the case, for the principle of limiting factors is 
always effective. The principle is generally recognized in the saying 
that a chain is no stronger than its weakest link and it is so universally 
11 161 



162 FUNDAMENTALS OF FRUIT PRODUCTION 

applied in everyday life that it is taken as a matter of course and 
consequently overlooked. 

The principle of limiting factors is particularly important for an 
understanding of the process of carbon assimilation and it has a direct 
practical application in the use of fertilizers. These two subjects are 
discussed in the following pages. 

CARBON ASSIMILATION 

The synthesis of organic compounds in plants depends on the assimi- 
lation of an element which occurs in and is characteristic of all organic 
compounds, namely, carbon. This element is provided by the carbon 
dioxide of the air, which, together with water absorbed by the roots, 
furnishes the materials for the synthesis of carbohydrates. These 
compounds contain more potential energy than those from which they 
are formed; this energy is supplied by the sun, whose radiant energy is 
transformed into the potential energy of carbohydrates by means of the 
green pigments of the leaf, the chlorophylls. The reaction or reactions 
by which water and carbon dioxide in the presence of light and through 
the agency of chlorophyll form carbohydrates and oxygen depend on two 
other factors, namely, enzymes and temperature which affects the rate of 

all chemical reactions. 

Factors Involved 

The rate of carbon assimilation depends on six factors: 

1. The supply of carbon dioxide. 

2. The supply of water. 

3. The intensity, duration and quality of light. 

4. The amount of chlorophyll. 

5. Temperature. 

6. The amount of enzymes. 

Carbon Dioxide. — The carbon dioxide content of the atmosphere is 
practically constant, varying little from 3 parts in each 10,000 of air. 
Carbon dioxide enters the leaf mainly through the stomata, though the 
epidermis with its cuticle is slightly permeable to it. Hence the diffu- 
sion of carbon dioxide into the leaf depends on about the same factors as 
the outward passage of water vapor, namely, the number of stomata, the 
rate at which carbon dioxide is utilized within the leaf and the condition 
of the air outside the leaf, whether it be moving or still. 

The amount of carbon dioxide assimilated has been shown to depend 
on the number of stomata on the upper and the lower surfaces of the leaf. 
For example, Table 58 shows the relation in leaves illuminated on the 
upper surface. In leaves with stomata confined to one surface the cor- 
relation of assimilation to number of stomata holds, but with leaves 
bearing stomata on both surfaces there is more intake of carbon dioxide 



MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 163 



Table 58. — The Relation of Carbon Dioxide Assimilated to the Number of 

Stomata in Leaves Illuminated on the Upper Surface 

(After Brown and Escombe 22 ) 





Stomatal ratio 
Upper surface 
Lower surface 


CO2 assimilated 
Upper surface 
Lower surface 




100 





100 
100 
119 
100 
269 


100 


Catalpa bignonioides 






Colchicum speciosum 


100 
100 


Rumex alpinus 


72 
100 
144 



than might be expected from the number of stomata on the upper side. 
This is because the leaves were illuminated from above, resulting prob- 
ably in a greater degree of opening of the stomata and a more rapid 
utilization of carbon dioxide by this side of the leaf. Both of these 
factors would favor a more rapid intake of carbon dioxide. 

The large amount absorbed by a leaf during active assimilation 
despite the low partial pressure of carbon dioxide in the atmosphere and 
the small fraction of the leaf surface occupied by stomata is explained 
by Brown and Escombe's law 21 which states that diffusion through a 
perforated membrane is proportional to the diameter of the apertures and 
not to their area. Because of the small size of the stomata, their great 
number and their distribution over the surface, the amount of carbon 
dioxide that theoretically could be taken in by the leaf under the most 
favorable circumstances is much greater than any observed quantity 
absorbed. Some idea of the amount used by leaves is given by an experi- 
ment of Brown and Escombe 22 on the sunflower, in which they found 
that approximately half a liter of carbon dioxide was used by each square 
meter of leaf surface in an hour. 

The carbon dioxide content of the atmosphere is constant; therefore 
it is not a factor to be considered in fruit growing. However, when it 
is artificially changed, in the absence of other limiting factors, the rate 
of assimilation increases in proportion to an increase in the carbon dioxide 
supply until an atmospheric concentration of 30 to 50 per cent, is reached. 
Cummings and Jones 36 have obtained very marked results from aerial 
fertilization with carbon dioxide. Legumes fertilized in this way showed 
increased carbohydrate storage and an increased production of pods 
and beans. Potatoes produced better tubers and strawberries showed 
distinct effects. This probably holds until an atmospheric concentration 
of about 30 per cent, or more is reached. Atmospheric concentrations 



164 FUNDAMENTALS OF FRUIT PRODUCTION 

of 50 per cent, carbon dioxide have a narcotic effect and depress assimi- 
lation. Changes in the rate of assimilation in so far as they depend on 
carbon dioxide supply are affected only by those factors that determine the 
rate of intake. This is increased by movement of the air, by the degree 
of stomatal opening and by any factors increasing the rate of utilization. 

Water. — The water supply of plants is treated in a preceding section 
and no further discussion need be added here. However, it must not be 
forgotten that water is one of the materials out of which carbohydrates 
are made. 

Light. — In the absence of limiting factors and particularly of high 
temperatures and extremely high light intensities, carbon assimilation 
increases with the intensity of light. Under such circumstances equal 
areas of different plants, equally illuminated, produce the same amounts 
of carbohydrates. There is evidence that at the intensities of the different 
wave lengths in the solar spectrum, red light is the most and green the 
least effective for photosynthesis. 

Light acts indirectly on carbon assimilation by raising the tempera- 
ture of the leaf and by stimulating the guard cells of the stomata to 
open, thus increasing the absorption of carbon dioxide. 83 

Leaf Pigments. — The chloroplasts of all green plants contain four 
pigments, two green and two yellow. They are: 

1. Chlorophyll a, blue-black in the solid state, green-blue in solution. 

2. Chlorophyll b, green-black in the solid state, pure green in 
solution. 

3. Carotin, forming orange-red crystals. 

4. Xanthophyll, forming yellow crystals. 

In the fresh nettle leaf, these four pigments occur in the following 
quantities, chlorophyll a, 24 parts in 12,000; chlorophyll b, 9; carotin 2 
and xanthophyll 4. 103 

In the chloroplast these pigments occur in a colloidal mixture with fats, 
waxes and salts of fatty acids. The chlorophyll content of leaves varies from 9.6 
to 1.2 per cent, of the dry weight. Shade leaves have a higher chlorophyll 
content than sun leaves in terms of dry weight, but not in proportion to leaf 
surface. The yellow pigments comprise 0.1 to 1.2 per cent, of the dry weight and 
there is no higher percentage in shade leaves than in sun leaves. There is no 
diurnal fluctuation in the amounts of the pigments, the mean ratio of chloro- 
phyll a to chlorophyll b being 2.85:1. On the whole, shade leaves con- 
tain less chlorophyll a than other leaves, their ratio of chlorophylls being 
2.93: 1. Less difference in this ratio is found in real shade plants like the beech 
than in plants that are ill adapted to growth in the shade. The mean ratio of 
carotin to xanthophyll for ordinary leaves is 0.603 : 1 and for shade leaves 
0.421 : 1. Xanthophyll is relatively more abundant in shade leaves. 

Variation ivith Age. — The chlorophyll content of leaves increases 
with age; so also the assimilatory power of the leaf, though not in the 



MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 165 

same degree. Hence, it appears that mature leaves contain an excess 
of chlorophyll and some other factor limits the rate of assimilation. 
In autumn the chlorophyll content decreases but as chlorophyll is not 
usually the limiting factor, assimilation does not decrease in proportion 
at first. If leaves remain green, they maintain their assimilatory power 
until they fall — a matter of no small importance in food storage. 

Variation icith Light Supply. — The development of chlorophyll in most 
plants depends on the action of light in which the red rays seem the most effect- 
ive. 33 ' 189 In all probability precursors of chlorophyll are present and exposure 
to light effects certain chemical reactions necessary for the complete development 
of the pigment. Light is not always essential to chlorophyll development, how- 
ever, for conifer seeds germinate and become green even in the dark. 

Light not only aids in the development of chlorophyll but at higher intensities 
brings about its destruction probably through oxidation. The decomposition of 
chlorophyll occurs outside the plant as well as within its tissues. This can be 
demonstrated by exposing a test tube containing a solution of chlorophyll to 
the light and comparing it with another kept in darkness. Red and yellow 
light are most effective in destroying chlorophyll. Consequently it is found 
that at low light intensities plants grown in yellow light contain the most chloro- 
phyll but that at higher intensities plants grown in blue light contain the most, 
owing to the destructive effect of the yellow light at these higher intensities. 205 
Similar effects from red light have been observed. 184 The double effect of light 
in stimulating the development of chlorophyll and in bringing about its destruc- 
tion, leads to noticeable differences in the chlorophyll content of plants growing 
in different latitudes and altitudes. It has been found that the minimum amount 
of chlorophyll necessary for growth is approximately the same at all latitudes 
but that the maximum amount increases toward the equator. 126 Hence, a 
plant may have twice as much chlorophyll in the tropics as at 60° north latitude. 
For a given species, however, the amount is less at both extremes of its range 
than at the center and it has been suggested that this may be due to greater 
oxidizing action at the limit on the equator side where the light would be more 
intense. The significance of these discoveries lies in the relation of carbohydrate 
accumulation to fruitfulness. Plants growing at high altitudes contain less 
chlorophyll than those growing in the lowlands. 97 In Alpine plants carbon assimi- 
lation requires greater light intensities but lower temperatures. 

Temperature. — At low and medium temperatures in the absence of 
other limiting factors, the rate of assimilation is a coefficient of the tem- 
perature. Assimilation has been detected at — 6°C. and from this point 
to 25°C. the rule stated above has been found to hold with the plants 
investigated. Above 25°C, the rate of assimilation does not remain 
constant at any given temperature. The higher the temperature, the 
more rapidly it decreases; at any given temperature the initial decrease 
is greatest. This "time factor" that enters at higher temperatures 
probably is indicative of the interference of another factor, namely, 
enzymes. 



166 FUNDAMENTALS OF FRUIT PRODUCTION 

Enzymes. — Assimilation is an enzyme reaction. Enzymes are 
organic catalytic substances that accelerate the rate of a reaction. Their 
chemical composition is unknown and their existence is shown only 
by their activity. They are not used up in a reaction, remaining after 
the process is completed. A minute amount of enzyme can effect the 
formation of a relatively large amount of end product; however, this 
is proportional to the amount of enzyme present. The effects of tem- 
perature described above are characteristic of enzyme reactions. The 
time factor manifesting itself at temperatures above 25°C. is not due 
to any direct effect of the temperatures on assimilation, but may be 
due to the permanent inactivation or decomposition of enzymes at 
high temperatures. Under these circumstances the rate of assimilation 
would decrease because the amount of enzyme diminished. The longer 
the temperature acted, the more enzyme would be decomposed. Simi- 
larly the narcotic effect of strong concentrations of carbon dioxide and 
the harmful influences of high light intensities are attributable in part 
to their effects on the assimilatory enzymes. Such adaptations as 
different species may show in their ability to assimilate best at higher 
or lower temperatures or light intensities probably are attributable to 
differences in their enzymes. 

The principle of limiting factors applies to the six factors determining 
carbon assimilation. 15 If any one factor is limiting, the rate of assimila- 
tion cannot be increased by any other. The carbon assimilation of green 
plants is usually limited by the seasonal variation in temperature and the 
diurnal variation in light. When temperature and light are both favor- 
able, the supply of carbon dioxide is probably the limiting factor. 36 
Water may be a limiting factor either through a direct effect on assimila- 
tion or indirectly by closing the stomata and so shutting off the supply 
of carbon dioxide. 

Products 

The products of photosynthesis are oxygen and carbohydrates. 

Oxygen. — The relation between the amount of oxygen evolved in the 
process of carbon assimilation and the amount of carbon dioxide taken in 
is not accurately known. When the respiration of the assimilating 
tissue is evaluated, it appears that the volume of oxygen evolved is prac- 
tically equal to, or very slightly greater than, the amount of carbon dioxide 
absorbed. The path by which oxygen escapes from the leaf is the same as 
that by which carbon dioxide enters or water vapor is lost, namely, 
through the intercellular spaces and the stomata. Oxygen is used in 
respiration, however, and when assimilation proceeds very slowly, the 
oxygen given off by assimilation may be entirely consumed by respiration. 
Similarly the carbon dioxide evolved by respiration may just about equal 
that used in assimilation under these circumstances. 



MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 167 

Carbohydrates. — What carbohydrate is the first product of carbon 
assimilation, is not known. Assuming it to be glucose, the reaction may 
be written as follows: 6C0 2 + 6H 2 + light + chlorophyll = C 6 H 12 6 
+60 2 . 

Simple, naturally occurring carbohydrates may contain five or six 
carbon atoms and are called accordingly pentoses or hexoses. There are 
two pentoses of common occurrence, arabinose and xylose; neither of these 
has been shown to be formed directly by assimilation. Four naturally 
occurring hexoses are known: glucose, fructose, mannose and galactose. 
Besides these simple sugars, there are compound sugars made up of 
two or more molecules of the simple, less one or more molecules of water. 
The disaccharides yield two molecules of simple sugars on hydrolysis. 
The two most common disaccharides are sucrose (cane sugar) which 
yields one molecule of glucose and one of fructose when hydrolyzed by 
dilute acids or inverted by an enzyme and maltose (malt sugar) which 
yields two molecules of glucose. 

In addition to the sugars there are complex carbohydrates, called 
polysaccharides; these yield an indefinite number of molecules of simple 
sugars on hydrolysis. They are for the most part less soluble in water 
than the sugars. One kind of sugar or a mixture of different kinds may 
be formed on hydrolysis. If the predominant sugar produced is a hexose, 
they are called hexosans; if a pentose, pentosans. 

Hexosans are classified according to the nature of the predominating 
sugar produced on hydrolysis. Thus there are glucosans which include 
starch, soluble starch, dextrin and cellulose; fructosans such as inulin; 
mannans, a constituent found in the wood and leaves of the lime, apple 
and chestnut, and galactans such as agar-agar. Pentosans include gums, 
mucilages and pectins, on which the jelling properties of fruit depend. 
The relationships of the carbohydrates are shown diagrammatically in 
Fig. 17. 

Daily and Seasonal Fluctuation in Leaves. — Though no reliable data 
are available on which to base a detailed picture of the carbohydrate 
changes in the leaf, the following statements may be made. 103 Hexose 
sugars and sucrose increase during the day, reach a maximum about mid- 
day, after which the quantity present decreases; these changes closely 
parallel the temperature variations and probably the variations in light 
intensity. There is no diurnal fluctuation in the amount of pentoses or 
of pentosans. As a result of the accumulation of sugars, starch is formed ; 
the process occurs only in cell plastids, either in chloroplasts which are 
green or in leucoplasts which are colorless. Species vary greatly in their 
capacity to form starch. Many plants — the onion, for instance — form 
none at all. Starch and sucrose formation in the leaf are only temporary. 
The carbohydrates are continuously conducted from the leaf as hexoses, 
which occur in greater amounts than other sugars in the conducting 



168 



FUNDAMENTALS OF FRUIT PRODUCTION 



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MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 169 

tissues. The starch present in the leaf accumulates there only because 
the manufacture of sugars is proceeding more rapidly than their removal. 
During the night the starch is digested by enzymes to maltose and the 
maltose to glucose, which then passes out of the leaf. 

The seasonal variation in the carbohydrate supply of leaves has been 
studied by Michel Durant. 134 He distinguishes two stages in the life 
of a leaf: (1) a period of carbohydrate synthesis and polymerization, 
extending from the time the leaves begin to function until the end of 
summer or in annual plants until the seeds begin to develop, during 
which period carbohydrate assimilation is active and carbohydrates of all 
types increase in amount; (2) a period of hydrolysis and simplification 
beginning about the time when the leaves turn yellow. This is marked 
by a decrease in the amount of compound carbohydrates and a further 
accumulation of simple sugars. The development of the abscission layer 
at the base of the leaves of deciduous plants is correlated with this 
accumulation of simple sugars in the leaf blade, so that their removal 
to the branch is soon stopped. The sugars increase until they are re- 
spired, fermented or washed out by rain. In leaves of annual plants, a 
larger proportion of these sugars is removed to the developing seeds and 
fruits; consequently, accumulation of simple sugars is less pronounced 
than in tree leaves. Nevertheless, at the end of this second period 
there are always appreciable amounts of carbohydrates left in the leaf. 

In evergreen leaves, the accumulation of simple sugars in the fall 
and winter is accentuated by photosynthesis which continues and pro- 
duces appreciable effects because cold weather retards respiration more 
than photosynthesis. Starch disappears or persists in small amounts 
and disaccharides containing fructose, such as sucrose, are prevalent. 
In the spring, starch is resynthesized at the expense of soluble sugars. In 
June, the polysaccharides of the leaves decrease, being added to stores 
in the branches or used in the development of the fruit. The carbohy- 
drate content remains low until the end of autumn. In general, the older 
the leaf, the greater its carbohydrate content and a maximum in poly- 
saccharides corresponds to a minimum in simple sugars. 

It has been found that the pentosans form a larger and larger propor- 
tion of the matter insoluble in alcohol and that the pentoses increase as 
the season advances, the latter probably representing hydrolytic products 
of pentosans. 62 

The entire plant depends on the assimilating function of its leaves 
for its supply of carbohydrates and of those compounds manufactured 
from them. The carbohydrates synthesized in the leaves are trans- 
located as hexoses through the phloem to all parts of the plant where they 
are either stored or utilized in ways specified later. 

Forms of Storage. — Since starch is the most common form in which 
carbohydrates are stored, it is important to consider the structure of the 



170 FUNDAMENTALS OF FRUIT PRODUCTION 

starch molecule in order to gain some idea of the factors involved in its 
formation. When starch is hydrolyzed slowly, it yields maltose and 
dextrin. Both of these yield glucose on further hydrolysis. Corn 
starch contains palmitic acid, a fatty acid and a related unsaturated 
compound. These fatty substances are liberated only after hydrolysis 
and are probably attached to the carbohydrate of the starch molecule. 183 
There is enough fatty acid in the corn starch molecule to make com- 
mercially profitable, in the manufacture of glucose from corn starch, 
the use of this residue as soap stock. Moreover, starch probably is not 
chemically homogeneous. At least two substances with distinct prop- 
erties have been separated and called amylose and amylopectin. 

When the concentration of hexoses is sufficiently great, starch is 
usually formed in the plastids. In fact, leaves of plants such as the 
onion which do not ordinarily form starch, will do so when floated on a 
10 per cent, solution of fructose. 

Starch will be formed, therefore, whenever the concentration of 
sugars reaches a certain point and other conditions such as temperature 
permit. In the summer and early autumn, starch is stored in the 
branches. In the peach, great amounts are found in the leaf gaps. In the 
younger apple shoots, it accumulates predominantly in the pith, being 
especially abundant at the nodes. 

The association of fat with the starch molecule indicates that the 
latter is the starting point for fat formation in plants. Fatty oils there- 
fore may be considered as a reserve food derived from carbohydrates 
especially in fruits like the avocado, in the seed of fruits like the apple 
and cocoanut and also over the winter in the younger roots and branches. 
Fats are esters which yield on hydrolysis one molecule of glycerine and 
three molecules of fatty acids. The commonest fatty acids found in 
plant fats and oils are: (1) oleic acid, in olive oil, almond oil, quince oil, 
cherry-, plum-, peach- and apricot-kernel oil; (2) linolic acid, in the oils 
from pumpkin, watermelon, melon, apple, pear and orange seeds; (3) 
palmitic acid, in cocoanut oil and cocoa butter and (4) dihydroxystearic 
acid, in grape-seed oil. Fats contain less oxygen in proportion to the 
carbon present in the molecule than carbohydrates. They, therefore, 
yield more energy when oxidized and may be regarded as concentrated 
energy in chemical combination. 

Sucrose and even glucose must at times be considered forms of carbo- 
hydrate storage. 

Seasonal Fluctuations of Stored Carbohydrates. — The seasonal varia- 
tion in the carbohydrate content of plants gives evidence of storage. 

Easily Hydrolyzable Carbohydrates. — Leclerc du Sablon's 122 deter- 
minations of the easily hydrolyzable carbohydrate in the roots and 
branches of the pear and chestnut are given in Table 59. This type of 
carbohydrate which includes sugars, starch and other easily hydrolyzed 



MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 171 



Table 59. — Easily Hydrolyzed Carbohydrate in Percentages of Dry Weight 

in Pear and Chestnut Trees 122 

Pear 



Date 


Branches 


Roots 


Feb. 18 


23.0 
21.3 
23.7 
24.7 
25.7 
25.4 


39.3 


Apr. 13 


22.4 


June 16 


27.9 


Aug. 4 


29.2 


Sept. 24 


33.8 


Dec. 1 


29.3 






Chestnut 


Jan. 11 


24.7 
24.7 
21.5 
19.9 
20.4 
21.1 
25.9 
26.4 
24.7 
23.0 


27.2 


Feb. 26 


25.7 


Mar. 28 


24.7 


May 20 


19.8 


June 22 


21.8 


July 27 


24.3 


Sept. 12 


30.3 


Oct. 19 


29.1 


Nov. 22 


28.9 


Dec. 12 


27.3 







polysaccharides, but not crude fiber, is at a maximun in September 
and at a minimum in May. Moreover there is a steady increase from 
May to September and a fairly steady decrease from September to May. 
Similar data showing the variations in the easily hydrolyzed polysac- 
charide of 7-year old apple trees are given in Table 60. Here also much 

Table 60. — Easily Hydrolyzed Carbohydrate in Percentages op Dry Weight 

in 7-year Old Apple Trees 23 

(Each figure is the average of analyses from two trees) 



Dormant, 
Dec. 3 



Buds 


In 


Growth 


swelling, 


bloom, 


over, 


Apr. 20 


May 18 


July 12 






30.54 


30.31 


19.21 


25.22 


29.38 


13.24 


26.59 


35.75 


11.68 


32.26 


31.58 


18.48 


30.03 


31.29 


16.08 


25.07 


34.08 


17.80 


32.23 


38.38 


21.77 


28.90 


36.47 


36.47 


31.87 



Leaves 
falling, 
Oct. 12 



New growth 

1-year old branches . 
2-year old branches 
3-year old branches . 
4-year old branches . 
5-year old branches . 

Trunk 

Large roots 

Small roots 



21.36 
22.13 
22.41 
20.44 
20.43 
25.83 
29.90 
29.36 



27.34 
26.50 
26.72 
26.10 
27.88 
27.28 
27.96 
32.02 
33.88 



172 



FUNDAMENTALS OF FRUIT PRODUCTION 



the same picture is presented except an increase from December to April, 
accounting for which is difficult. The minimum in May is apparent, but 
the maximum in September does not appear, as samples were not collected 
at that time. 

In all the data presented, the roots have shown a higher percentage 
and a greater fluctuation in carbohydrate than the shoots. However, 
this does not indicate a greater absolute carbohydrate content. Esti- 
mates by Curtis 37 indicating the probable relationships at the time of bud 
swelling (April) are shown in Table 61. According to these figures the 

Table 61. — Estimated Number op Pounds of Carbohydrate in Tops and Roots 
of a 7-year Old Apple Tree 37 

1 year twigs 1.10 Large roots 5.71 

Older branches 5 . 89 Small roots 2 . 43 

Trunk 5.25 



Total 13.24 Total 8.14 

portions of a tree above ground contain half again as much as the roots. 
The conditions found in apple spurs are shown in Table 62. These 
figures evidently are comparable to the data of Le Clerc du Sablon on the 
pear and chestnut. 

Table 62. — Total Carbohydrate (not Including Crude Fiber) of Apple Spurs 100 
(In percentages of dry weight) 



Bearing (average 
of three trees) 



Non-bearing 

(average of two 

trees) 



March. . 
May 13 
June 25 
Sept. 2. 
Nov. 19 
Jan. 24. 




The increase in carbohydrate from May to September is explained by 
the assimilatory activity of the leaves. The decrease from September 
to May must be attributed to several factors. The major part is due to 
the use of carbohydrates for the formation of other substances — probably 
of nitrogenous compounds which increase in September and of fatty 
substances, which are discussed presently. The decrease in carbo- 
hydrate is also in part the result of consumption in respiration, which 
proceeds from September to May, but most actively after growth has 
begun and in part the result of translocation into the newly developing 
leaves, flowers and eventually fruits. Hence the lower minimum in the 






MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 173 

carbohydrate content of bearing spurs in May may be associated with 
flowering. The higher maximum in these same spurs in September is 
probably connected with the development of specialized tissues in the 
purse during fruit development. 

The study of the various types of carbohydrate, particularly starch 
and sugars, shows similar seasonal fluctuations despite some variation. 

Starch. — The only analytical data on the seasonal variation in starch 
content are on spurs. In woody tissues, starch is a relatively small 
fraction of the total polysaccharides, but probably a significant fraction 
of the available carbohydrates. Figure 18 shows the starch variations 
in bearing, non-bearing and barren spurs of the apple. 100 




Fig. 18. — Starch content of apple spurs in percentages of dry weight; bearing spurs 
represented by continuous lines, non-bearing spurs by broken lines and barren spurs by 
dot-dash lines. (After Hooker. 100 ) 



There are two maxima for starch and two minima. This was shown 
microchemically by Mer and d'Arbaumont. 133 The maximum in Septem- 
ber and the minimum in May correspond to the maximum and minimum 
for total carbohydrates. The second minimum in January and the 
second maximum in March are due to conversion of starch to sugars and 
a resynthesis of starch in spring just before vegetation commences. The 
second maximum is not, however, so high as the first — except in bearing 
spurs — which indicates that a certain amount of carbohydrate has been 
consumed in respiration or used for the formation of other substances. 
Determinations of the ether extract permit an estimate of the fat and oil 
content and show that fats increase during the winter. The previous 
discussion of the structure of starch indicates that this is the point 



174 



FUNDAMENTALS OF FRUIT PRODUCTION 



of departure for fat formation. Table 63 shows the seasonal variation 
in ether extract in 7-year old apple trees. It is evident that the younger 
the tissue, the more fat it contains and that the fat content is at a maxi- 
mum just before active growth begins and at a minimum after active 
growth is over. 

Table 63. — Ether Extract in Percentages of Dry Weight in 7-year Old Apple 

Trees 23 
(Each figure is the average of analyses from two trees) 






Dormant, 
Dec. 3 



Buds 
swelling, 
Apr. 20 



In 
bloom, 
May 18 



Growth 

over, 
July 12 



Leaves 
falling, 
Oct. 12 



New growth 
1-year branches 
2-year branches 
3-year branches 
4-year branches 
5-year branches 

Trunk 

Large roots 

Small roots 



3.26 
2.77 
2.49 
1.75 
1.28 
0.85 
2.25 
6.79 



5.18 
3.58 
2.92 
1.50 
1.07 
0.96 
1.86 
5.03 



5.00 
3.03 
2.39 
1.57 
1.14 
0.79 
2.02 
4.06 



3 


15 


2 


68 


2 


31 


1 


99 


1 


31 


1 


18 





72 


2 


38 


5 


85 



4.11 
3.01 
2.92 
2.71 
1.07 
0.91 
0.70 
1.31 
6.55 



Characteristic differences between the starch content of bearing 
and non-bearing spurs appear in Fig. 18. In winter the spurs with 
fruit buds have more starch. Moreover starch accumulation commences 



































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Fig. 19. — Total sugar content of apple spurs in percentages of dry weight; bearing 
spurs represented by continuous lines, non-bearing spurs by broken lines and barren spurs 
by dot-dash lines. {After Hooker. 100 ) 

in non-bearing spurs in May and in bearing spurs in June. This differ- 
ence is connected with carbohydrate utilization by the fruit. The 
relation of this to fruit bud differentiation is discussed later. 

Sugars. — The seasonal variation in the sugar content of spurs is 
shown in Fig. 19. The rapid drop in sugar during the spring is explained 



MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 175 

by respiration, translocation to the leaves and fruit, and utilization in the 
formation of complex carbohydrates. The assimilatory activity of the 
leaves soon restores the sugar content of the spurs, but a marked increase 
does not commence until September. This is due to continued demands 
for sugar by the developing fruit on bearing spurs and to starch accumula- 
tion in non-bearing spurs. The increase in sugars after September is 
associated with the decrease in starch during this period and represents a 
partial conversion of starch to sugars. Some of this sugar is sucrose, 
a form in which carbohydrate is stored during the winter, as the figures 
in Table 64 show. 

Table 64. — Average Non-reducing Sugar Content of Spurs in Percentages 

of Dry Weight 100 





Bearing 
spurs 


Non-bearing 
spurs 


Barren 
spurs 


March 

May 13 

June 26 


0.59 
0.44 
0.00 
0.09 
1.27 
0.56 


0.47 
0.27 
0.05 
0.45 
0.77 
2.40 


0.97 
0.45 
0.19 


Sept. 2 

Nov. 14 

Jan. 24 


0.35 
0.91 
1.66 



The sugar used in the development of fruit is considerable, as Table 
65 indicates. In the apple, the percentage and absolute amounts in 
the fruit increase steadily, the rate of increase becoming greater as 
maturity approaches. This holds for prunes also. 181 In pears the 
percentage decreases at first and then increases, while the absolute 
amounts increase steadily. In either case the increase in absolute 
amount extends to the end of August or the middle of September. 

Michel Durant 134 points out that a period of carbohydrate synthesis followed 
by one of hydrolysis and simplification is found in fruits as well as in leaves. 
Ripe fruit therefore contains more sugar than unripe fruit. The increase in the 
sugar content may continue even after the fruit is picked. This occurs in drying 
prunes when sugar is formed by the hydrolysis of starch. If prunes after 
removal from the tree are exposed to the sunlight for 2 or 3 days, their sugar 
content increases, but after 5 days' exposure their sugar is rapidly consumed in 
respiration and fermentation. 181 

In recapitulation, it is emphasized that the carbohydrate supply 
of the plant is manufactured in the leaves and that the leaves supply the 
entire plant. In consequence, movement of carbohydrate is usually 
away from the leaves to the growing points, cambium and storage organs. 
Carbohydrate is stored mostly in the immediate vicinity of places where 
it may later be used. Thus the work of Magness 128 andof Curtis 37 indi- 



176 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 65. — Reducing Sugar Content of Developing Apples and Pears 149 



Date 



Apples 



Pleissner 
Rambour 



Per- 
centage 
of dry 
weight 



Grams 

in 1,000 

fruits 



Red Easter 
Caville 



Per- 
centage 
of dry 
weight 



Grams 
in 1,000 

fruits 



Date 



Pears 



Salzburg 



Liegel's Honey 



Per 

eentage 
of dry 
weight 



Grams 
in 1,000 

fruits 



Per- 
centage 
of dry 
weight 



Grams 

in 1,000 

fruits 



June 2. . 
June 12. 
June 22. 
July 2 . . . 
July 12.. 
July 22 . , 
Aug. 1 . . 
Aug. 11. 
Aug. 21 . 
Aug. 31 . 
Sept. 10. 
Sept. 20. 
Sept. 30. 
Dec. 12. 



3.05 


0.9 


3.28 


0.7 


10.70 


22.0 


6.75 


8.8 


14.91 


97.0 


12.70 


43.0 


22.90 


368.0 


16.51 


150.0 


24.19 


870.0 


19.78 


370.0 


17.11 


1,150.0 


20.29 


670.0 


39.45 


2,540.0 


23.19 


950.0 


34.65 


4,260.0 


26.42 


1,400.0 


39.69 


4,250.0 


30.17 


1,740.0 


43.07 


6,600.0 


31.47 


2,400.0 


51.28 


7,530.0 


35.41 


3,040.0 


60.04 


10,850.0 


36.28 


3,550.0 


52.99 


9,630.0 


33.73 


3,200.0 






48.14 


4,730.0 



May 26 
June 5 . 
June 15. 
June 25. 
July 5. . 
July 15. 
July 25. 
Aug. 4 . . 
Aug. 14. 
Aug. 24 . 
Sept. 3 
Sept. 8 . 



4.98 

2.17 

1.66 

1.92 

2.78 

4.56 

7.16 

16.43 

30.03 

35.02 

51.35 



1.0 

2.7 

7.7 

18.0 

36.0 

95.0 

218.0 

637.0 

1,660.0 

2,230.0 

3,590.0 

4,180.0 



0.8 

3.6 

10.2 

32.0 

68.0 

175.0 

536.0 

770.0 

1,520.0 

1,800.0 



cate that the carbohydrate stores in the roots do not return to the tops. 
They are used by the roots. Cambial activity depends on the carbo- 
hydrate stored in the medullary rays and the starch sheath. Bud 
development in the spring depends largely on the carbohydrate stored 
in the pith or leaf gap near the bud. 

CARBOHYDRATE UTILIZATION 

Carbohydrates are used in any one of the following ways: 

1. For tissue building, that is for the construction of other carbo- 
hydrates, or of different substances manufactured from carbohydrates, 
which enter into the composition of plant cells. 

2. For the retention of moisture. 

3. To increase osmotic concentration. 

4. As a source of energy. 

In Tissue Building. — According to Czapek, glucose is a constituent 
of every living cell and therefore may be considered a necessary part 
of the chemical equipment of living matter. The great value of glucose 
in metabolism is probably associated with the ease with which it is altered 
to a number of different but related compounds. Through its enolitic 
form it may be changed to fructose and mannose. Glucose, fructose 
and mannose exist in at least five forms each. Wherever glucose is 
present in solution, as in protoplasm, certain of these forms — depending 






MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 177 

on the prevailing conditions — tend to develop until a complex equilib- 
rium is established. Since each form has different physical and chemical 
properties the multiplicity of ways in which glucose may become the 
basic material for a great diversity of physiological processes is evident. 
Besides the forms in which glucose may be stored temporarily, it is utilized 
for the construction of the permanent framework of the plant, being 
the substance from which many forms of carbohydrate as well as of 
other groups of organic compounds are made. The cellulose wall is 
secreted by each cell from its supply of hexose sugars. So also is the 
middle lamella, which is a pentosan, a salt of pectic acid. It has been 
suggested that fats probably are derived from carbohydrates and that 
starch is presumably an intermediate stage in fat formation. Glucosides 
give rise to one or more molecules of sugar on hydrolysis and it is shown 
presently that organic acids arise from the respiration of carbohydrates. 
Little is known concerning the seasonal quantitative variation in 
many of these contituents. It may be said, however, that crude fiber, 
which is composed chiefly of cellulose and lignin increases steadily with 
age in roots and branches and that seasonal variations are insignificant 
in comparison to this regular trend. 

Complete vegetative development depends on an adequate carbohydrate 
supply and a plant is unable to attain its full size and ordinary shape in dark- 
ness or particularly in the absence of red light. This is true especially of leaves. 
If they are supplied with carbohydrates in a form in which they can be absorbed, 
the effect of the absence of light on the size of the leaf can largely be eliminated. 
However, different plants show more or less characteristic responses to an ab- 
sence of light in this respect, which seems to be associated with the amount of 
carbohydrate that tends to accumulate when the leaves are kept in darkness. 
Bean leaves, for example, contain small amounts of carbohydrates when kept 
in the dark; consequently the leaves do not grow. This is the case with most of 
the fruit plants. In a certain number of plants such as wheat, starch is always 
present in the leaves and considerable amounts of carbohydrate accumulate 
even when the leaves are kept in darkness; these attain their usual size under 
such conditions, though they may be narrower than the leaves of illuminated 
plants. 146 There are, however, other peculiarities in the form and structure of 
plants grown in darkness which cannot be attributed in any way to the carbo- 
hydrate supply. 

In Retaining Moisture. — Pentosans have, according to Spoehr, 177 
the property of holding moisture. Certain pentosans develop under 
conditions where the moisture supply is limited and furnish the plant 
with a water-retaining mechanism which minimizes the effect of the water 
deficiency. The moisture held by pentosans seems to be in a colloidal 
mixture, where it is retained tenaciously and offers resistance to desic- 
cating agencies. This colloidally held water should be differentiated 

from free water since it is characterized by distinct physical properties. 
12 



178 FUNDAMENTALS OF FRUIT PRODUCTION 

Increasing Osmotic Concentration. — Sugars are important to the 
plant because they are osmotically active. Since the osmotic concen- 
tration depends on the number of molecules and not on their size, it is 
evident that the formation of disaccharicles from simple sugars reduces 
the osmotic concentration. Conversely, the hydrolysis of compound 
sugars or polysaccharides to simple sugars increases the osmotic concen- 
tration. Thus the building up and splitting down of carbohydrates 
regulates the osmotic concentration. On the other hand, it unques- 
tionably plays an important part in controlling synthetic and hydrolytic 
processes. Thus compound sugars and especially starch are usually 
produced wherever the concentration of sugars is high, though other 
factors are involved, particularly enzymes. The hydrolysis of compound 
carbohydrates proceeds most rapidly when the concentration of sugars 
is low; therefore their consumption in respiration, their removal to other 
organs and their use in the formation of other compounds, particularly 
of substances like cellulose that are insoluble and consequently not 
involved in the osmotic system, accelerate the processes of hydrolysis. 

As a Source of Energy. — One of the most important properties of 
carbohydrates is that of yielding energy in the process of respiration. In 
fact most of the energy used by plants and animals is the stored potential 
energy of fats and carbohydrates. By means of carbohydrates the roots 
are able to utilize the energy of sunlight. 

Respiration involves several processes. There are many theories, but 
according to the most suggestive, respiration consists of two main reac- 
tions; one is a process of cleavage, in which the simple carbohydrate 
molecule is split into carbon dioxide and certain intermediate substances, 
probably alcohols or acids; the other is a process of oxidation, in which 
these intermediate substances are oxidized to carbon dioxide and water. 
The first process is essentially a fermentation for which the enzyme, 
zymase, is essential. The second process — of oxidation — depends on 
enzymes called peroxidases which act only in the presence of peroxides. 
Peroxidases supposedly transfer oxygen from organic peroxides to the 
products of cleavage formed during the first process in respiration, 
oxidizing them to carbon dioxide and water. According to some investi- 
gators there are other enzymes involved but if this be true, they play 
subsidiary parts and need not be considered here. 

In general the amount of carbon dioxide given off is approximately 
equal to the amount of oxygen used in respiration so that the respiration 
of a hexose may be represented by the formula C 6 Hi 2 6 + 60 2 = 6H 2 
+ 6C0 2 + energy. The two processes of respiration, cleavage and 
oxidation, are more or less independent of each other, so that an accumu- 
lation of acid may oCcur in plant tissues during periods of active respira- 
tion, through the incomplete oxidation of carbohydrates and other sub- 
stances. The inverse correlation existing between starch content and 



MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 179 

acidity in apple spurs is shown in Figs. 20 and 21. In the spring, starch 
and sugar decreased rapidly in these spurs and acidity rose. This may be 
interpreted as indicating the hydrolysis of starch to sugar and the incom- 







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Fig. 20.- 



-Starch, reducing sugar content and titratable acidity of bearing apple spurs 
compared. (After Hooker. 100 ) 



plete oxidation of the sugar to acid. Some of the decrease in sugar is 
explained by removal to the developing leaves and flowers. The increase 
in acidity in the spring lasted longer and reached a higher maximum in 























































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Fig. 21. — Starch, reducing sugar content and titratable acidity of non-bearing apple spurs 
compared. (After Hooker. 100 ) 

bearing spurs. At the same time the consumption of reducing sugars 
was more complete. This may be associated with greater respiratory 
activity in flowers. Respiratory activity is particularly pronounced 
in floral parts, germinating seeds and growing parts in general. 



180 FUNDAMENTALS OF FRUIT PRODUCTION 

Relation to Pigment Formation. — A supply of carbohydrates is necessary for 
the development of certain pigments in leaves, flowers and fruits. Laurent 116 
showed that fruit pigments are of two types; some develop only as a result of 
direct exposure to light; others do not require direct illumination of the fruit 
but for their development the leaves must be able to manufacture carbohydrates 
and the connection between the leaves and the fruit must not be interrupted. 
Kraus 113 suggests that pigments of both sorts occur in apples. The effect of 
low temperature or parasitic attack in increasing the pigmentation of fruit or 
leaves is attributed to an attendant accumulation of sugars, especially glucose, 
fructose and sucrose. 

Summary. — The elaborated plant foods used in tissue building are 
manufactured from the nutrient materials obtained from the soil and air 
at a rate depending principally on (1) the available supply of the several 
materials including water, (2) the intensity, duration and quality of the 
light reaching the plant, (3) the amounts of the green leaf pigments, 
(4) temperature and (5) the presence of certain enzymes. Any of these 
factors of the plant's environment or composition may become limiting 
in plant food synthesis, their degree of importance varying with condi- 
tions. The immediate products of photosynthetic activity of the plant 
are oxygen and carbohydrates. Oxygen for the most part is set free 
and is in effect a by-product. Glucose is assumed to be the first synthetic 
product of photosynthesis. Glucose may be considered a starting point 
for the formation of more complex substances, such as the other hexoses, 
disaccharides, polysaccharides, pentosans and pentoses. Starch is the 
most common form in which carbohydrates are stored. They are also 
stored frequently as sugars and sometimes they are transformed into 
fats. The seasonal distribution of the more important of these materials 
is discussed. Their storage is more common in or near the organs where 
they are later used. Carbohydrates are used principally for new tissue 
building, for the retention of moisture, for increasing osmotic concentra- 
tion and as a source of energy. Glucose particularly is a basic material 
in the construction of plant tissues; for a great diversity of physiological 
processes, pentosans are particularly important because of their water- 
retaining capacity. Sugars are important in determining osmotic 
concentration. Carbohydrates supply energy in the process of respira- 
tion. The formation of certain pigments also depends on carbohydrates. 



CHAPTER X 

THE INITIATION OF THE REPRODUCTIVE PROCESSES 

The initiation of the reproductive processes of the plant should be 
considered in the light of chemical conditions and the concurrent mor- 
phological changes. 

THE DEVELOPMENT OF THE FRUITFUL CONDITION 

There is much evidence that conditions associated with carbohydrate 
accumulation have an important relation to fruitfulness in plants. 

The Response of the Plant to Changes in Relative Amounts of 
Nitrogen and of Carbohydrates. — Kraus and Kraybill 115 , studying the 
effects on the tomato of various treatments, found that striking differences 
in chemical composition and in behavior with respect to fruitfulness and 
vegetative growth could be produced by controlling the environmental 
conditions. They summarize their work as follows: 

"1. Plants grown with an abundant supply of available nitrogen and the 
opportunity for carbohydrate synthesis, are vigorously vegetative and unfruit- 
ful. Such plants are high in moisture, total nitrogen, nitrate nitrogen and low in 
total dry matter, free reducing substances, sucrose and polysaccharides. 

"2. Plants grown with an abundant supply of nitrogen and then transferred 
and grown with a moderate supply of available nitrogen are less vegetative but 
fruitful. As compared with the vegetative plants, they are lower in moisture, 
total nitrogen, and nitrate nitrogen, and higher in total dry matter, free reducing 
substances, sucrose and polysaccharides. 

''3. Plants grown with an abundant supply of nitrogen and then transferred 
and grown with a very low supply of available nitrogen are very weakly vegeta- 
tive and unfruitful. As compared with the vegetative plants, they are very much 
lower in moisture and total nitrogen and are lacking in nitrate nitrogen; they 
are much higher in total dry matter, free reducing substances, sucrose, and poly- 
saccharides." 

Three typical effects, measured principally in terms of total nitrogen, 
carbohydrate and moisture have been produced by these three distinct 
environments. The first is characteristic of vigorous vegetative growth. 
"An abundance of moisture and mineral nutrients, including nitrates, 
coupled with an available carbohydrate supply, makes for increased 
vegetation, barrenness and sterility." 115 ! The second condition represents 
a readjustment through which the plant must pass before it becomes 
fruitful. "A relative decrease in nitrates in proportion to the carbo- 
hydrates makes for an accumulation of the latter; and also for fruitful- 

181 



182 FUNDAMENTALS OF FRUIT PRODUCTION 

ness, fertility, and lessened vegetation." 115 The third condition, in 
which "a further reduction of nitrates without inhibiting a possible 
increase of carbohydrates, makes for a suppression both of vegetation and 
fruitfulness," 115 is evidently the manifestation of the effect of a limiting 
factor, nitrate supply. In addition to these three, a fourth condition 
was found. "Though there be an abundance of moisture and mineral 
nutrients, including nitrates, yet without an available carbohydrate 
supply, vegetation is weakened and the plants are non-fruitful. . . . 
The available carbohydrate supply or the possibility for their manu- 
facture or supply, constitute as much a limiting factor in growth as the 
available nitrogen and moisture supply." 115 

Those instances (3 and 4), in which nitrogen or carbohydrate supply 
are limiting factors of growth, reveal the necessity of a proper balance 
between carbohydrate and nitrate supply for the best vegetative 
development. 

"In other words, this experiment indicates first, that the limitation of the 
nitrates resulted in the suppression of growth and the accumulation of the more 
complex carbohydrates; second, that the limitation of the carbohydrates, even 
with large quantities of available nitrates" in the soil, results in a suppression of 
growth; third, that a rapid vegetative extension results from an adjustment of 
the carbohydrates and nitrates relative to one another so that both may be 
utilized in the formation and expansion of such structures ; and fourth, that such 
a relationship can be secured either by increasing the nitrates without decreasing 
the carbohydrates, or by decreasing the carbohydrates without increasing the 
nitrates. While it is apparent that the amounts of these compounds relative to 
one another would be the same in both the above cases, the total amounts would 
be greater in the former and less in the latter, a condition faithfully reflected 
in the amount of growth produced." 115 

In this passage Kraus and Kraybill show that there is a distinct 
nutritive relation between the supply of nitrates and of carbohydrates, 
for vegetative growth and development. A carbohydrate supply 
is therefore not only just as essential for the manufacture of protoplasm 
as are nitrogen and the essential mineral elements, but it combines 
with them in definite proportion for the building up of the plant tissue. 

The Significance of Carbohydrate Accumulation. Manufacture in 
Excess of Utilization. — The differences between the conditions char- 
acteristic of vigorous vegetative growth which is unfruitful and vegeta- 
tion accompanied by fruitfulness are of interest. There is no evidence 
to show that the utilization of nutrient substances is any different in a 
plant showing fruit bud differentiation from that in one which does not, 
or that the nutritive relation between carbohydrate and nitrate supply 
in particular is altered. Kraus and Kraybill's work shows that, in so 
far as the materials determined by them are concerned, the chief differ- 



THE INITIATION OF THE REPRODUCTIVE PROCESSES 183 

ence is associated with circumstances making for carbohydrate accumula- 
tion in fruitful plants rather than a difference in the method of carbo- 
hydrate utilization. In other words, the carbohydrate supplied must be 
in excess of the amount used. 

Carbohydrate accumulation depends primarily on light conditions. Under 
experimental conditions carbohydrate assimilation varies with light intensity, 
in the absence of other limiting factors ; however, other factors become limiting 
for plants grown in the open, so that carbohydrate assimilation and hence car- 
bohydrate accumulation depends on the number of hours of sunlight rather than 
on the light intensity. 156 Garner and Allard 71 have shown experimentally that 
an increase in the duration of light exposure determines fruitfulness in some plants 
and they suggest that the daily increase in duration of illumination which reaches 
a maximum on June 21, may have an important relation to the time at which 
these plants blossom. It is interesting to observe that fruit bud differentiation 
in the apple usually occurs the latter part of June or early part of July, though 
it has been observed to occur at almost every season. However, Garner and 
Allard found that many plants do not blossom unless the duration of light exposure 
is short. Voechting 192 found that a decrease in light intensity reduced the number 
of blossoms and eventually prevented flowering altogether in some plants, while 
in others there was a tendency for the development of cleistogamous flowers. 

Klebs 110 found that when blossoming depends on the intensity of illumination, 
red light which is the most effective in photosynthesis is essential, blue light 
having much the same effect as darkness. 

Defoliation previous to the period of fruit bud differentiation obviously 
interferes with carbohydrate manufacture and the recent work of Harvey 90 shows 
that this is reflected in the chemical composition of defoliated apple spurs which 
contain less hydrolyzable polysaccharides and total carbohydrates than normal 
spurs. This is particularly important in connection with the decreased fruit 
bud differentiation observed by Harvey on defoliated fruit spurs. 

In Fruit Spurs. — Hooker 100 in a study of the seasonal changes in the 
chemical composition of apple spurs of certain varieties and bearing 
habits found that, when there was a relatively low total nitrogen content, 
starch accumulation occurred while fruit buds were being differentiated. 
When there was a relatively high total nitrogen content, starch accumula- 
tion did not occur at the same time, though it followed later, and the 
spurs remained vegetative for another year. These conditions were 
found in spurs showing characteristically different behavior regardless 
of whether spurs of only one or of several different bearing habits were 
found on the same tree at one time. Some of these results, shown 
graphically in Figs. 22 and 23, emphasize two principles involved in the 
development of the fruitful condition; (1) At certain critical periods in the 
life of the plant, its activities are directed into one channel or another, 
depending on the nature of the conditions affecting its equilibrium at that 
particular time. This lends weight to Kraus and Kraybill's surmise 



184 



FUNDAMENTALS OF FRUIT PRODUCTION 



that "the conditions for the initiation of floral primordia and even bloom- 
ing are probably different from those accompanying fruit setting." In 
fact, recent work by Murneek 90 shows that the conditions favoring fruit 



4 






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Fig. 22. — Nitrogen, phosphorus and starch contents of bearing apple spurs compared. 
The arrow indicates the season when fruit bud differentiation would occur in non-bearing 
spurs. (After Hooker. 100 ) 

setting in apples are quite different from those determining fruit bud 
differentiation. (2) Different parts of a plant may act quite indepen- 
dently of one another, depending on the local factors affecting them. 























































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Fig. 23. — Nitrogen, phosphorus and starch contents of non-bearing apples purs compared. 
The arrow indicates the season of fruit bud differentiation. (After Hooker. 100 ) 

Influence of the Nitrate Supply. — When the nitrate supply was varied 
in Kraus and KraybuTs experiments the amount of carbohydrate utilization 
varied with it, in accordance with the nutritive relation between carbo- 



THE INITIATION OF THE REPRODUCTIVE PROCESSES 185 

hydrates and nitrates. Hence, in the absence of any other limiting 
factors for vegetative development, the balance of carbohydrate manu- 
facture over utilization depends on the nitrate supply. When this is 
kept high, though carbohydrates are manufactured in large quantities, 
they are immediately utilized for vegetative development and the plants 
are unfruitful and vigorously vegetative. If the nitrate supply is reduced 
moderately, carbohydrate utilization is checked and there is opportunity 
for carbohydrate accumulation; fruitfulness follows. To be sure carbo- 
hydrate accumulation occurs when the nitrate supply is still further 
reduced, but here the situation is complicated because nitrate then 
becomes a limiting factor to fruitfulness by inhibiting such vegetative 
development as appears necessary for fruit bud differentiation. Plants 
of this type are stunted and altogether lacking in nitrate nitrogen. 

Influence of the Moisture Supply. — Nitrate supply is not the only factor 
which may determine the balance of carbohydrate manufacture over 
utilization. This may be accomplished also by a decrease in any other 
factor involved in the process of growth and development. For example, 
Kraus and Kraybill report that "withholding moisture from plants grown 
under conditions of relative abundance of available nitrogen results in 
much the same condition of fruitfulness and carbohydrate storage as 
the limiting of the supply of available nitrogen." A diminution of the 
water supply is well known to be frequently associated with fruitfulness. 
In this case, as in that of nitrate supply, there is probably a limit beyond 
which a further reduction of the water supply results in unfruitfulness 
and stunted growth. 

Influence of Other Factors. — Klebs 111 concluded from numerous investi- 
gations that a reduction in the supply of nutritive salts leads to the fruit- 
ful condition provided there be adequate facilities for photosynthesis 
and hence for carbohydrate accumulation. Recent work of Walster 193 
has shown that heat may be a limiting factor to vegetative development 
as well as water or any of the essential nutrient and food materials and 
that diminished heat, even with a high nitrogen supply, leads to carbohy- 
drate accumulation and culm formation in barley. These investigations 
indicate that any environmental factor may check growth and lead to 
carbohydrate accumulation and that fruitfulness may result provided 
vegetative development is not seriously retarded or altogether stopped. 
It is shown later in this section that vigorous vegetative growth is not 
inimical to fruitfulness. On the contrary, the facts just presented indi- 
cate that fruitfulness and vegetative development are associated functions. 

FRUIT-BUD FORMATION 

Since carbohydrate accumulation seems associated with fruit bud 
differentiation and the conditions for carbohydrate accumulation change 
during the season, it is evident that there must be considerable variation 



186 FUNDAMENTALS OF FRUIT PRODUCTION 

in the time when fruit buds are formed. A knowledge of the approximate 
time when their differentiation occurs is of fundamental importance, 
particularly in connection with possible means of influencing their number 
by cultural treatment. Furthermore, the stage of advancement in which 
the fruit buds enter the winter is shown elsewhere to have an important 
relation to winter injury. 

For many years flower buds of the ordinary deciduous fruit trees 
have been known, in a rather indefinite way, to have their inception in 
the summer previous to their opening; more exact knowledge is compara- 
tively recent and is even now rather incomplete. 

. Investigation of the apple has been more extensive than is the case 
with the other fruits; there is, however, enough similarity between them 
to permit the use of the apple as the type. One difference, however, 
between buds of apple and those of some of the other fruits, pointed out 
elsewhere, should be borne in mind. The fruit bud of the apple is, with 
trivial exceptions, a mixed bud, containing leaves and blossoms; in the 
other type, as the peach, fruit buds contain no leaves. 

Evidence of Differentiation. — The growing point of the apple shoot or 
spur presents a rounded surface surrounded by embryonic leaves and it is 
characterized by its relatively large amount of meristematic tissue. 
Sooner or later its aspect changes, taking one of two forms. 

In one case the change consists principally in the greater breadth of 
the surface with a somewhat smaller degree of convexity and in the 
absence of the swellings at the periphery that in the actively growing 
shoot precede the formation of a rudimentary leaf. The amount of 
meristematic tissue becomes relatively smaller. The growing point is 
at the resting stage; surrounded by protective scales and embryonic 
leaves, it constitutes the leaf bud. 

In the alternative case the growing point differentiates into structures 
that form the essential part of the flower or fruit bud. The first evidence 
of differentiation in this direction is the rapid elevation of the crown or 
surface of the growing point into a narrow conical form, rounded at the 
apex, with the fibro-vascular connections and pith areas advancing 
concurrently. In the axils of the young leaves within the bud appear 
other protuberances which soon become blunt at the top. At the same 
time other leaf primordia develop rapidly higher in the spiral in which 
they appear and in turn younger protuberances (the floral primordia) 
appear in their axils. The apical protuberance, destined to become the 
central (terminal) flower of the cluster, is differentiated last; however, 
when it does take shape it is already larger than those previously laid 
down. It soon takes and thenceforth maintains the lead in development 
over the other flower primordia (see Fig. 24). 

Whether a bud which has entered the resting stage as a leaf bud, can, 
without a renewal of growth, develop into a fruit bud later the same 



THE INITIATION OF THE REPRODUCTIVE PROCESSES 187 

season is a matter obviously difficult of determination. Indirect 
evidence, however, points to this possibility and suggests that fruit buds 
may be initiated at any time when conditions are favorable. It is 
certain that a spur after forming a leaf bud may start into second growth 
and then form a fruit bud, all during the same growing season. 

Magness 127 has traced the development of axillary buds. He finds that: 
"axillary buds originate very close to the tip or apex of rapidly growing shoots. 
As the shoot elongates, the leaves are given off at the side of the growing point, 
and the young bud appears first as simply an undifferentiated mass of rapidly 
dividing cells in the axils of these leaves ... no primordia were found de- 
veloping in the axils of leaves that were not fairly well formed. 

"The buds developed very rapidly and those subtended by half-grown leaves, 
1 to 2 inches above the terminal, were well differentiated, with a growing point or 
apex, and bud scales being rapidly formed. The cells of the growing tip were 
not well differentiated and this, with the high staining reaction of this region, 
indicated that much growth was still taking place." By July 9 some of the older 
axial buds had nearly reached the condition in which they would pass the winter. 

Time of Differentiation. — Drinkard 63 reported that fruit bud differ- 
entiation in the Oldenburg apple occurred about June 20 in Virginia. 
Goff 75 found the first clear evidence in the Hoadley apple on June 30 in 
Wisconsin. Bradford 17 in Oregon found similar stages during the first 
10 days of July, though resting stages of leaf buds were apparent in May. 
The earliest differentiation observed by Kirby 109 in Iowa was about the 
first of July. 

In the pear it was observed in Virginia in samples of Kieffer taken 
about the middle of July, somewhat later than the initial period for the 
apple. 63 In Wisconsin evidence was found in the Wilder Early on July 
21. 75 Albert first found differentiation in the pear early in August 
In the Champion quince Goff found embryonic flowers in bud examined, 
late in the autumn, but did not determine the exact period of their 
inception. Albert found differentiation in the Japanese quince in August. 
In the Luster peach initial stages of flower formation were observed in 
Virginia the first week in July; 63 Quaintance 151 in Georgia found no 
indication of differentiation in Demming's September peach on June 14, 
but on July 23 he reported: "the embryo flower is well under way 
and the calyx lobes are quite pronounced." Apparently, then, the initial 
stages must have occurred late in June. Goff, 76 working with a 
Bokhara peach, considered that "flowers began to form about the middle 
of September the past season." At Davis, California, the first evidence 
of differentiation in the almond has been reported as about Aug. 18. 182 

The plum as investigated by Drinkard shows some variation in the 
time of initiation of fruit buds. Whitaker, one of the Wildgoose group, 
gave no evidence until the first week in September; "observations on sev- 
eral varieties of Japanese plums showed that the initial formation of fruit 



188 FUNDAMENTALS OF FRUIT PRODUCTION 

buds occurred during the second week in July; and the individual fruit 
buds within the cluster were clear and distinct on August 7th." 63 In 
Wisconsin, flower formation has been found under way in the Aitken plum 
on Aug. 9 and some differentiation in the Rollingstone on July 8 in 1899 
and on July 5 in the following year. 75 

In the Louis Phillippe cherry of the Morello group, signs of differ- 
entiation have been noted on June 30 in Virginia. Goff, working with 
the King's Amarelle cherry, found the earliest indications of flowers 
on July ll 75 and in the following year on July 8. At Heidelberg, 
Germany, blossom primordia of the sweet cherry were visible during 
July. 84 

Investigations of flower-bud formation in the small fruits were 
made by Goff. In the strawberry Sept. 20 was the date of the first 
indication of flower buds. 76 

Differentiation was found to occur in the Pomona currant about 
July 8 and in the Black Victoria currant about Aug. 3. 77 In the Down- 
ing gooseberry there was evidence on Aug. 30; in the cranberry no clear 
signs were found until Sept. 16. Less definite observations were made 
in raspberries and blackberries; nevertheless, unquestionable evidence 
shows that the flowers are formed the year previous to blossoming. 
"In the raspberry and blackberry," states Goff, "the buds that form 
in the axils of the leaves of the young shoots contain a whole branch in 
embryo — often several nodes, with a leaf at each node. The bud at 
the apex of this branch and the axillary buds along it, if they form, are 
flower-buds . . . embryo flowers in those buds are formed the season 
before their expansion, at least in part. " 

Fruit bud formation in the grape occurs during the summer previous 
to blossoming. A single bud contains in embryo a shoot with blossom 
primordia. General observations to this effect are recorded by Goff 77 
and Bioletti 13 but no precise determination of the time is available. 
Behrens 12 states that the first shoot primordia appear concurrently with 
the first swelling of the buds in which they develop (mid-June). Since 
these are laid down continuously through the summer many stages are 
present on a vine at any one time. Subsequently the blossom primordia 
appear. The buds laid down late in the season are likely to be arrested 
in their development before the formation of blossom primordia occurs. 
Behrens emphasizes the importance of early differentiation in securing 
a crop for the following season. 

In the filbert (Corylus Avellana) Albert 1 found signs of catkins on 
June 10, before embyronic leaves were laid down; female blossoms were 
not found until early in September. In the beech he was unable to 
find blossom buds until the beginning of leaf fall, but since the pollen 
mother cells in the anthers had already formed, differentiation must 
have occurred much earlier. 



THE INITIATION OF THE REPRODUCTIVE PROCESSES 189 

In Relation to Position. — Not all fruit buds are differentiated simul- 
taneously, even on the same tree. Investigations by Goff 76 convinced 
him that in the apple and pear fruit-bud formation may occur after the 




Fig. 24. — Stages in fruit bud development of the Yellow Newtown apple. Above, to 
the left Sept. 10, to the right Nov. 25; below, to the left Feb. 14, to the right Mar. 6. 
(After Bradford. 17 ) 



first of September; he suggested as alternatives either (1) two periods 
of flower formation or (2) a continual differentiation through the season. 
Bradford, working with the Yellow Newton apple, reports least variation 
in spurs which have borne previously but are not bearing in the current 



190 FUNDAMENTALS OF FRUIT PRODUCTION 

season (see Fig. 24) ; terminal fruit buds on long shoots obviously must be 
differentiated at a later period than is known to characterize formation 
on spurs. Considerable variation in the time of differentiation occurs 
also in young spurs which have never before formed fruit buds. Even in 
bearing spurs, when they form fruit buds, the formation may occur from 
early July to late August. Spurs which had blossomed during the current 
season but failed to set fruit varied still more; some of the earliest 
differentiation observed was found in spurs of this class and later differ- 
ention also occurred. 

Magness 127 in a careful study of axial buds found resting stages of 
leaf buds in several varieties as early as July 9 and early in September 
he recognized differentiation into flower buds. Some of his preparations 
taken in December suggest an initial differentiation into fruit buds, 
though he evidently did not regard them as such. In the Tetofski apple 
he considered some differentiation to have occurred about the first of 
August. He states that a spur bud of July 23 showed as much develop- 
ment as the most advanced axillary buds of Sept. 2. In the investi- 
gations of the following year the "main period of axillary fruit-bud 
formation in the varieties studied began after August 1, and a great 
many buds were apparently being differentiated on September 8. This 
was fully one month later than spur buds on the same trees." 

Direct comparisons of the time of differentiation in buds of stone 
fruits in different positions are not available. Roberts, 158 however, 
finds in September a difference in the development of buds on sour 
cherries according to their positions on the 4- or 5-inch shoot. This 
difference suggests that flower formation is initiated first both in the basal 
and in terminal regions. It is probable that a similar condition occurs 
in the peach. 

Goff 76 found little or no difference in the comparative develop- 
ment of flower buds in rooted runners and parent plants in the 
strawberry. 

Varietal Differences. — Bradford 17 found considerable difference be- 
tween varieties of apple in the stage of development attained early in 
August, indicating a lack of uniformity in the time of differentiation. 
Of the varieties observed, Stark, Red Astrachan and Oldenburg seemed 
farther advanced than Jonathan, Northern Spy and Grimes. The 
season of ripening of the fruit appears to make little difference in the 
time of differentiation; there appears to be, however, some correspond- 
ence, though not absolute, between the order of blossoming and the order 
of differentiation. Magness 127 found White Pearmain, Tetofski and 
Yellow Transparent noticeably advanced in development in early July 
as compared with Lady and Jonathan. 

Goff 77 found considerable difference between varieties in the time 
of fruit-bud formation, some forming fruit buds before Aug. 1 while some 



THE INITIATION OF THE REPRODUCTIVE PROCESSES 191 

were considered to form none until after the first of September. Differ- 
ences between varieties of plums have been mentioned earlier. 

Differences Induced by Cultural Treatment. — Kirby 109 notes an earlier 
differentiation of fruit buds in apples growing in sod than in the same 
varieties in cultivated soil. Still finer distinctions were noted. 

"The earliest time," he states, "at which flower buds were formed occurred 
on clover sod, with a low percentage of soil moisture. Flower buds formed 
earlier on a clover sod than on a blue grass sod having slightly less soil moisture. 
On the other hand, flower buds formed earlier on a blue grass sod than on a clover 
sod having about 2.5 per cent, more soil moisture. These facts indicate two 
things ; first, that the addition of nitrates in the clover sod causes the flower buds 
to form earlier ; and second, that the amount of soil moisture is a very important 
if not the chief external factor in determining the time at which flower buds form. 

"The formation of flower buds began about the first of July on the plots 
where it occurred earliest and extended until the middle of September on the 
plots where it occurred latest, thus occupying a period of about 2>£ months. 
The time occupied by each tree in forming flower buds was about 4 weeks." 

The time of differentiation in the Baldwin apple in New Hampshire 
has been found somewhat variable, suggesting the effect of influences 
proceeding directly or indirectly from weather conditions. 14 

Goff 77 supplied water to a 9-year old Gideon apple tree in a dry season. 
Comparison on Aug. 9 with a similar unwatered tree showed very little 
difference in the stage of development reached at that time, though buds 
on the non-watered tree were somewhat more advanced. 

In the sour cherry very strongly growing shoots and shoots partly 
defoliated by shot-hole fungus were retarded in their development. 158 
Buds on younger, trees were less advanced than those on older trees of 
the same variety. Since these studies were made at the approach of 
winter they do not furnish conclusive evidence as to the time of differen- 
tiation. However, they harmonize with the available direct evidence. 

Abnormalities. — Finally, the occurrence of the so-called second 
bloom should be noted. Paddock and Whipple 143 mention a case of 
this kind. Similar teratological variations reported by Daniel were 
attributed by him to excessive pruning. This occurrence has been 
attributed at times to late frosts which destroyed the first blossoms and 
induced the formation of another set. This may be a correct explanation 
in some instances. The occurrence of blossoms on the vegetative shoots 
of several spurs bearing fruit in normal position was noted in an Olden- 
burg apple at Columbia, Mo., in 1920; the following year the same tree 
showed this phenomenon in about 20 per cent, of its spurs before any 
injurious frost occurred. Whether these buds were differentiated the 
preceding season cannot be stated positively. However, in the Rome 
Beauty apple vegetative shoots from fruiting spurs were observed to 
grow to a length of 4 to 6 inches, forming 6 or 7 leaves and then — 
still early in the season — to open solitary blossoms. In this case differ- 



192 FUNDAMENTALS OF FRUIT PRODUCTION 

entiation undoubtedly occurred in the spring. Hand pollination in some 
cases resulted in the formation of fruits with seeds of normal appearance 
and in Oldenburg without such assistance a considerable proportion 
of the crop actually harvested developed from secondary bloom. 

Apple trees in tropical climates, though they blossom little, seem not 
to be restricted in the time of fruit-bud formation. 

The conclusion seems warranted that a fruit bud may be formed 
at any time, though ordinarily the period is rather restricted. The 
period evidently can be varied somewhat by cultural treatments, includ- 
ing perhaps any practice that modifies the rate of growth. In general 
the earlier the period of differentiation, the greater the number of fruit 
buds finally formed, but as shown elsewhere, with some qualifications, 
the less hardy those buds are. 

Winter Stages. — Kraus 114 has described in detail the development of 
the individual flower within the bud. The sepals are differentiated first, 
followed closely by the primordia of the petals. Either simultaneously 
with, or directly after, their appearance those of the stamens are laid 
down; after these come the primordia of the carpels. The ovules do not 
appear until the resumption of growth in the spring. 

During November and December in Virginia, Drinkard 63 found 
little development of the gross parts of the apple flower but noted some 
cytological changes. "During December," he states, "the pollen 
mother cells developed large, prominent nuclei. . . . Nearly all changes 
which occurred during the month of January took place in the stamens. 
. . . On February 19, there was some indication of renewed develop- 
ment in the anthers; these had enlarged appreciably on February 24. 
. . . Early in March there was a beginning of development of ovules 
in the cells of the ovary. These became very distinct by March 22. At 
the same time tetrad formation was going on in the pollen mother cells." 

Drinkard found some development during the winter in buds of pear 
also. In the peach, growth during winter seemed more active. The ovule 
appeared late in December and tetrad formation in the pollen mother cells 
late in January, in both instances considerably in advance of the apple. 
Similarly the plum was found to show more or less development, practi- 
cally throughout the winter. These observations are of interest in con- 
nection with the differences in hardiness of fruit buds discussed elsewhere. 

However, it has been reported that in New York fruit buds do not 
develop from the middle of November until about the first of March 204 
and in Wisconsin no evidences of activity were found from the beginning 
of freezing weather until after the middle of March. 75 In fact it was 
stated that there was no change in pear flowers from Dec. 1 to Mar. 30. 75 
Albert reports pear blossoms to be unchanged until March, though he 
records development in the pistils of the filbert during November and 
December. In Japanese quince he found that development is arrested 






THE INITIATION OF THE REPRODUCTIVE PROCESSES 193 

only during cold weather and is resumed whenever temperatures permit. 
Many of these blossoms are killed by cold. 

Magness 127 noted a difference in the stage of development of buds on 
spurs in successive years. Buds of the Tetofski apple in November, 
1914, showed ovules developed, while in December, 1915, they had not 
reached that stage. 

"The blooming season during the spring of 1915 was fully one week earlier," 
he states, "than that of 1916. It is quite probable that factors operating during 
the late summer and fall to hasten or retard flower development, as well as factors 
operating during the spring, materially influence the time of blossoming in our 
orchard fruits." This statement is of particular interest when correlated with 
Sandsten's work, discussed under Temperature Relations. 

Summary. — The available data do not permit a definite statement of 
the exact cause or causes of fruit bud differentiation or an exact de- 
cription of the internal nutritive conditions associated with fruitfulness 
and unfruitfulness. However, there must be at least two antecedents 
to an initiation of the reproductive processes: (1) There must be an 
excess of carbohydrates above the amount required for vegetative 
development. The rate of manufacture must exceed the rate of utili- 
zation. (2) There must not be any limiting factor that entirely stops 
vegetative growth which must continue within the bud even though there 
be no new shoots and leaves formed or even no visible indication of an 
increase in the size of the buds that are differentiating flower parts. In 
the orchard the supply of available nitrogen is probably the most common 
limiting factor. If nitrogen is present in large amounts it forces the rapid 
utilization of carbohydrates so that their accumulation cannot occur. If 
it is very limited in amount, growth is practically stopped before fruit 
bud differentiation can take place. Carbohydrate accumulation may 
not in itself be the cause of the fruitful condition in the plant as a whole 
or in its individual parts. It may simply be another result of the same 
factors that lead to fruitfulness; at least, however, the two are associated. 

In practically all the deciduous fruits growing in temperate climates 
fruit bud differentiation occurs during the summer or fall previous to the 
opening of the buds. Every bud that is formed may be considered a 
potential fruit bud, but practically differentiation takes place only when 
suitable nutritive conditions are provided. Ordinarily each bud develops 
to a certain point and then comes to a comparative rest. Later develop- 
ment is as a vegetative bud or a flower bud, depending on whether con- 
ditions do or do not favor differentiation of flower parts in the slow growth 
that takes place during the period of comparative rest. The exact time 
of differentiation varies considerably with variety, seasonal conditions, 
moisture supply, method of culture, position on the plant and other 
factors. In cold climates there are practically no changes within the bud 
during the winter. 

13 



CHAPTER XI 
SURPLUSES AND DEFICIENCIES 

Though much has been written on the function of individual mineral 
constituents, it is questionable whether definite roles can be assigned 
to them, except in so far as they enter into the composition of specific 
organic compounds that have known functions. Thus magnesium is a 
component of the chlorophyll molecule, which is essential for photosyn- 
thesis. It is important, nevertheless, to know the effects attending a 
surplus or a deficiency of one or more mineral elements, so that the symp- 
toms may be recognized and the condition corrected. However, patho- 
logical conditions found to follow an excess or deficiency of any one 
element do not necessarily indicate a direct relation of the element to 
the symptoms. Thus, though a deficiency of iron is known to produce 
chlorosis, a disordered condition in which chlorophyll does not develop, 
iron does not occur in the chlorophyll molecule. 

From the considerations in the previous chapters, it follows that 
either a surplus or a deficiency of any soil element may affect the plant 
by disturbing the balance between its various constituents. A defi- 
ciency of an element may also affect the plant when that element is a 
limiting factor of growth. In all cases, a surplus or a deficiency must be 
understood to mean an amount greater or less than that which is utilized 
along with the other elements of the soil. The effect of a surplus of any 
essential soil constituent must be upon the balance or equilibrium of the 
plant. There may be no effect, since the plant may adjust itself to a 
surplus which is merely tolerated. There is much evidence that the 
quantities of potassium and calcium in plant tissues are often much in 
excess of the amounts used in metabolism. The same undoubtedly 
holds for other essential and many non-essential elements such as sodium, 
chlorine, aluminum and silicon. On the other hand, distinct pathological 
conditions may ensue which lead eventually to the death of the plant. 
Likewise elements which are not essential to the nutrition of the plant 
may be tolerated or they may produce disturbances, the effects of which 
may be either to stimulate assimilation or to induce pathological con- 
ditions and eventually death. As a general physiological theorem, it 
may be stated that any substance which is toxic in certain amounts is 
stimulating in smaller amounts. 

SURPLUSES 
The evidences for the existence of pathological conditions due to the 
absorption of a surplus of some soil nutrient are practically limited to the 
cases of nitrogen and magnesium. 

194 



SURPLUSES AND DEFICIENCIES 195 

Nitrogen. — The results of an excess of nitrogen usually appear the 
year following the actual surplus nitrogen absorption. They are shown 176 
in trees by a tendency in the fruit to physiological decay. Dieback, 
or exanthema, and gummosis of citrus trees also are attributed to a 
surplus of nitrogen. 195 This causes a diseased condition in the growing 
tissues of the tree characterized primarily by gum pockets, stained 
terminal branches, "ammoniated" fruits, bark excrescences and multiple 
buds. The secondary symptoms are an unusually deep green color of 
the foliage, distorted growth of the terminal branches, frenching of the 
foliage and thick coarse leaves shaped like those of the peach. Mineral 
sources of nitrogen, even in great quantities, are not known to produce 
dieback though they may accentuate the symptoms in trees already 
affected, 67 but organic fertilizers containing nitrogen often lead to its 
development when they are applied in large amounts. 

Magnesium. — The poisonous action of an excess of magnesium 
absorbed by the plant is attended by a browning of the roots and of 
vessels in the wood, cessation of growth in the roots and eventually death 
of the root hairs, the entire roots and leaves. These toxic effects may be 
counteracted in large part by calcium through its antagonistic action on 
magnesium, previously discussed. It should be pointed out that toxic 
effects similar to those following an excess of magnesium have been 
observed to develop from oxalic acid and that the toxic effects of other 
salts and salt mixtures, such as potassium nitrate with potassium 
phosphate, may be corrected by calcium. 

Copper. — Of the effects of non-essential elements, those of copper are 
among the most striking. Copper salts are poisonous even in exceed- 
ingly small concentrations. Water distilled in copper receptacles is 
frequently toxic. Coupin 32 found that the lethal dose for grains grown 
in water culture was for each 100 cubic centimeters of nutrient solution, 
0.0049 gram copper bromide; 0.005 copper chloride; 0.0056 copper 
sulfate; 0.0057 copper acetate and 0.006 copper nitrate. Copper salts 
absorbed by the roots of the grape are likely to stop root growth. On the 
other hand, the stimulating effect of a mixture of copper sulfate and lime 
sprayed on leaves is well known. Leaf development is stimulated, the 
chlorophyll content increased, the palisade cells become longer and nar- 
rower and the spongy parenchyma has smaller intercellular spaces. 10 
Without doubt the amounts of copper absorbed by the sprayed leaves are 
less than those which produce toxic effects when absorbed by the roots. 
Ewert, 65 however, has demonstrated that concentrations of 1 to 100,000,- 
000 of copper sulfate are toxic to the pulp cells of the apple and that 
minute quantities entering through the stomata after spraying or taken 
up by the roots may result in one of the forms of bitter pit. If the con- 
tention 129 that copper is an essential nutrient be correct, then the observed 
effects may be the result of counteracting a limiting factor of assimilation. 



196 FUNDAMENTALS OF FRUIT PRODUCTION 

Arsenic. — Arsenic is another mineral toxic to plants in exceedingly 
small amounts. In many of the higher plants exposure to a concentra- 
tion of 1 part in 1,000,000 is sufficient to inhibit growth. 141 When arsenic 
is absorbed by the roots, they show its effects first. 

The toxic effects of arsenic on fruit trees are described in an article in the 
Horticulturist. 102 "When a little arsenic is introduced into the circulation of 
a fruit tree at that season (early spring) it first discolors the sap vessels of the 
inner bark, then the leaves suddenly flag, and droop; the branch shrivels and 
turns black; and finally if the dose is large enough, the whole tree dies." Stimu- 
lating effects from arsenic have been observed, presumably when absorption was 
restricted to amounts smaller than that indicated above as toxic. 

The question of the toxic action of arsenic is one of much interest 
since nearly all deciduous orchard fruits require one or more applications 
of arsenical sprays each year. In old bearing orchards the total arsenic 
used per acre each year is likely to be as much as 4 pounds, figured as 
arsenic trioxide. Though applied directly to the foliage and fruit, most 
of it reaches the ground in the course of the season. It is generally 
applied in some very insoluble and chemically inactive form, such as 
arsenate of lead. However, there is a considerable accumulation, espe- 
cially in the surface soil, as spraying is continued. This has led to con- 
siderable uneasiness among growers and much injury has been reported 
to be due to these accumulations in some of the irrigated sections. The 
injury has taken the form of collar and root rot and in addition it has 
often been followed by premature ripening of the fruit and wood in the 
fall and the death of the tree the following year. However, it is only in 
irrigated sections and in soils with a rather high alkali content that this 
trouble has been encountered. This suggests that the injury is attribu- 
table to the action of various alkali salts reacting with the arsenic to make 
it soluble, to the combined action of alkali salts and arsenic, or possibly 
to alkali salts alone, since similar injuries are known to result from alkali 
poisoning. Results with Ben Davis apple trees sprayed in one season with 
as much arsenic as ordinarily would be applied in 10 to 40 years and under 
conditions where soil alkali was not a factor, have led to the conclusion 
that such arsenical poisoning as has been reported from certain sections 
is not attributable to the arsenic. 8 Some of these applications were so 
heavy that the trees not only remained whitened all summer, but the 
"ground under the entire head of the tree was so saturated with the 
arsenic as to appear moldy white to a depth of 3 or 4 inches." No injury 
appeared in the trees or even in the vegetation (including strawberries, 
alfalfa and a number of weeds) under some of them. This makes it 
evident that little is to be feared from the toxic effect of the arsenic used 
in spraying unless the soil has a fairly high alkali content and then the 
problem is one of dealing with the alkali rather than with the arsenic. 
Arsenic is, however, a contributing factor. Ewert 65 believes that there is 



SURPLUSES AND DEFICIENCIES 197 

possibility of the absorption through the stomata and cuticle of the fruit 
of quantities sufficient to cause local poisoning in the apple, giving rise 
to the disorder known as bitter pit. 

Manganese. — The relation of an excess of manganese to iron deficit 
and the method of curing the diseased condition have been discussed. 
In excess, this element produces interesting symptoms, illustrated by 
pineapples grown on manganese soils. 

The root system is reduced by the death of a large percentage of the fine 
branched rootlets some months after their formation. The roots that remain 
alive have a superabundance of root hairs, almost every epidermal cell elongating 
into one, and also a blunt growing tip, about half as large as a lead pencil, 
frequently swollen into an enlarged fleshy end. The formation of these 
enlargements seems to mark the end of growth and death soon follows. The 
leaf has an irregular surface due to shrinkage from loss of water, producing 
prominences which become dark brown. The cells have brown walls and 
in some cases the protoplasm eventually disintegrates. The green cells thus 
lose their color, become plasmolized and in some cases the nuclei turn brown. 
Here also the protoplasm loses its granular structure and disintegrates. As a 
result of the lack of chlorophyll, the leaves contain limited amounts of starch, 
but at the base of the leaves, in the stalks and roots, starch is abundant, having 
been stored there before the decomposition of the chlorophyll. Frequently no 
fruit develops, but that which does is reddish pink, without a trace of green, 
undersized and excessively acid. 106 

Apparently manganese poisoning is rare in deciduous fruits. In 
very dilute amounts manganese has a stimulating effect. 19 

Other Elements. — Compounds of many other elements such as lead, 
mercury, zinc, boron 19 and silver are toxic in certain concentrations, but 
toxic effects from them are rare. However, these materials are known 
occasionally to be absorbed in considerable quantities — zinc for example 
up to 13 per cent, of the ash, mercury and copper up to 1 per cent. 65 
Ewert 65 has shown that extremely minute quantities of these, in con- 
centrations varying from 1 in 1,000,000 to 1 in 1,000,000,000, may 
cause local browning in the tissues of the fruit of the apple and induce the 
condition known as bitter pit. 

Mention may be made here of certain toxic gases such as hydrogen 
sulfide, sulfur dioxide, hydrogen cyanide and chlorine. Sulfur dioxide 
injury is of considerable practical importance because the damage done 
to vegetation by smelter fumes is due largely to this compound. 

The bulk of the evidence on the toxicity of inorganic mineral soil 
constituents that has been discussed, suggests that the effects are largely 
local in the plant. Amounts small enough to be stimulating are unques- 
tionably absorbed by the roots, or in the case of spraying, by the leaves, 
but amounts large enough to poison the plant seem to induce injury 
chiefly by affecting the absorbing organs. Hence cessation of growth 



198 FUNDAMENTALS OF FRUIT PRODUCTION 

and eventually death of the roots are the primary symptoms. Dis- 
orders proceeding from the causes just outlined should be distinguished 
from the toxic effects produced by organic compounds or by excessive 
soil concentrations, discussed previously. 

DEFICIENCIES 

The lack of a sufficient amount of any essential soil constituent may 
lead to the development of distinct pathological conditions; or it may 
result simply in checking vegetative development and fruit production 
without producing obvious pathological symptoms. The use of fertil- 
izers for correcting both of these conditions is discussed in the two 
following chapters in which particular emphasis is accorded the correc- 
tion of conditions interfering with fruit production on a commercial 
scale. The discussion immediately following concerns the more impor- 
tant pathological symptoms which are associated with the presence of 
unduly small amounts or with the complete exhaustion of essential 
mineral elements. 

Nitrogen. — A deficiency of nitrogen may become evident in several 
different ways. The plant may be dwarfed, though it develops com- 
pletely and produces flowers, fruits and seeds. As a rule, however, the 
leaves are pale green because of the relatively small amounts of chloro- 
phyll and the development of the mature fruit is affected in one way 
or another. There may be an incomplete development of the sexual 
organs, and consequent unfruitfulness; 170 in case fruits develop they may 
be seedless, as in apples, pears and grapes, 171 or the fruit may develop 
somewhat but drop prematurely. This is a common result of nitrogen 
deficiency in apples and pears. The latter sometimes show excessive 
thorn development in connection with a lack of nitrogen. 172 

Phosphorus and Potassium. — A deficiency of phosphorus appears 
to produce no characteristic symptoms. Chlorophyll development is 
not affected, but the plant does not increase in dry weight. 

A deficiency of potassium 172 is usually associated with a scarcity 
of carbohydrate reserves. In trees, the terminal shoots show weak 
development and eventually dry out, or shoot formation may be 
suppressed wholly. Plants suffering from a lack of potassium often 
maintain a healthy appearance longer than those lacking nitrogen or 
phosphorus. Whatever potassium is available apparently is used first for 
vegetative growth and development and, if there is no residuum, the plant 
does not blossom. Eventually the leaf blade becomes yellow on the 
edges and between the veins, then brown and finally white, while the 
veins and petiole remain green. This condition is known as a frenching 
of the foliage. A potassium deficiency renders the roots susceptible to 
rotting and the plant eventually dies. When nitrogen or phosphorus is 
deficient, plants are likely to remain alive longer in a stunted condition. 



SURPLUSES AND DEFICIENCIES 199 

Sulphur. — As a result of sulphur deficiency, cell division is retarded 
and fruit development is suppressed, 175 but the plant is able to develop 
vegetatively to a limited extent. 

Iron. — A lack of iron produces the well-known condition of chlorosis 
or yellows. This is not characteristic solely of iron want, for it may 
result eventually from a lack of either nitrogen or magnesium, but the 
effects of iron deficiency in producing chlorosis are more rapid than 
those of nitrogen insufficiency and consequently more striking. When 
iron is deficient, developing leaves are at first able to avail themselves 
of iron in older tissues. Later the new leaves are green only at the tips 
and eventually the newly developed leaves are entirely yellow. Chloro- 
plasts develop in them, but they contain no chlorophyll. Recent 
investigation 142 has shown that organic compounds containing the pyrrol 
ring, which appears in the structure of chlorophyll, correct the condition 
of chlorosis produced by iron want, suggesting that iron may have 
something to do with the formation of this ring. However, since iron is 
just as essential for fungi and other parasitic plants which have no chloro- 
phyll as for green plants, its importance cannot be limited to the part 
it apparently plays in the synthesis of the pyrrol ring. 

Magnesium and Calcium.— A. deficiency of magnesium 173 reduces 
fruit formation and eventually produces chlorosis. This is to be expected 
since magnesium is a constituent of chlorophyll. Cell division in the 
epidermis is also affected. 

A lack of calcium interferes with carbohydrate transportation and 
utilization, but does not stop its manufacture. These disturbances 
may be associated with the formation by calcium of insoluble salts with 
substances which are products of carbohydrate utilization, as oxalic 
acid. A lack of calcium would result in an accumulation of oxalic 
acid, which is toxic in solution. This might be expected to interfere 
with the processes of carbohydrate utilization. Root growth is retarded 
or stopped, an effect already mentioned as resulting from an excess 
of magnesium. Hence some of the effects of calcium deficiency may 
be associated with the resultant effect on the calcium-magnesium ratio. 124 

Chlorine. — Though chlorine is not an essential element, some mention 
should be made here of the effects of an absence of chlorine. There 
are conditions in the field under which the best development occurs 
only when chlorides are added to the soil. 60 Recent investigations show 
that the effects of chlorides are markedly different on different plants, 
but that in many cases they serve directly or indirectly as a fertilizer. 186 

AN ANALYSIS OF THE FERTILIZER PROBLEM 

The data that have been presented on the factors affecting soil 
productivity on the one hand and the metabolic processes going on within 
the plant on the other, emphasize the incompleteness of the knowledge 



200 FUNDAMENTALS OF FRUIT PRODUCTION 

of plant nutrition. Much important information has been obtained 
regarding changes occurring in the soil and something is known of the 
synthesis, translocation, storage and utilization of organic materials. 
At best, however, this information is fragmentary and much generali- 
zation regarding the use of fertilizers in the orchard is unsafe. Some 
idea of the complexity of the problem is obtained when we consider 
the numerous ways in which fertilizers may act: (1) to change conditions 
in the soil and (2) to disturb or restore equilibria within the plant. 
Among the more important of these methods of action may be mentioned 
the following: 

1. Altering the physical properties of the soil. 

2. Affecting the displacement (lyotropic succession) of various elements. 

3. Changing the solubility of other soil constituents. 

4. Changing the availability of other soil constituents. 

5. Changing the concentration of the soil solution. 

6. Changing the reaction of the soil solution. 

7. Influencing bacterial activity in the soil. 

8. Correcting or disturbing the balance between certain soil constituents, e.g., 
calcium and magnesium antagonism. 

9. Stimulating or checking chemical reactions in the soil or absorption by the 
roots. 

10. Acting as toxins or protecting against their influence. 

11. Serving directly as nutrients for the plant. 

12. Restoring or disturbing chemical equilibria within the plant after absorption. 

The Fertilizer Requirements of the Orchard. — In the discussion that 
has preceded some attention has been devoted to each of these factors 
in the nutrition of the plant. There has been presented also a general 
resume of some of the available information regarding synthesis, trans- 
location and use of certain plant constituents. Incidentally the following 
facts have been brought out: 

1. Many elements that evidently are not required are found in plants. 
Seldom are they harmful; they are merely tolerated. Among them may 
be mentioned silicon, aluminum, sodium, manganese, titanium and 
probably chlorine. These elements are not required in fertilizers. They 
may be combined with certain others that are of importance and they may 
have some indirect influence upon the physical condition of the soil or the 
chemical nature of the soil solution. They may often serve a useful pur- 
pose in furnishing some of the so-called "indifferent" ash and occasionally 
some distinctly beneficial response attributable to their presence may be 
obtained when they are carried in fertilizers, but on the whole they need 
not be given serious consideration in the problem of orchard fertilization. 

2. Certain elements are found universally in plants and are necessary 
constituents; however, except in very unusual cases, they exist in the soil 
in sufficient quantities and in forms sufficiently available to meet the 
requirements of orchard trees. The plant often takes up more than it 



SURPLUSES AND DEFICIENCIES 201 

uses. This surplus is merely tolerated and usually no harmful influence 
results. Among these elements may be mentioned potassium, calcium 
and magnesium. As with the preceding list, their application in fertilizers 
may indirectly benefit the plant through improving physical and chemical 
conditions within the soil, or restoring a proper ratio between them in the 
case of the last two. 

It would seem that sufficient evidence to support these statements has been 
presented in the discussion of the individual elements that has preceded. It is 
realized, however, that they run counter to the opinions that have been expressed 
in a great number of published statements dealing with this question, to many 
recommendations that have been made for the fertilization of fruit trees, to 
what has in some instances become more or less well established practice and to 
the apparent results of certain plot experiments. This is true particularly in the 
cases of potassium and calcium. It seems desirable, therefore, to bring together 
the results of some of the orchard fertilizer experiments with potash and lime 
and examine them somewhat critically. Table 66 presents such data gathered 
from many sources. It does not include all the records that might be assembled, 
but it represents the results of American plot trials. 

In some cases the application of potassium- or of calcium-carrying fertilizers 
has resulted in increased yields; in others in decreased yields. The increases 
outweigh the decreases in both number and amount; but in the Pennsylvania 
experiments alone, of those included in the table, are the increases striking or 
to be regarded as of considerable significance. These particular Pennsylvania 
records are extremes purposely chosen from a large number, the great majority 
of which show no such marked response from potash applications. Furthermore, 
the different check plots in these two orchards show such variation as to justify 
some hesitancy in drawing conclusions when comparing the results of one fer- 
tilizer treatment with those of another on a plot some distance removed from 
the first. For instance, it may be questioned if the plots treated with lime alone 
and with nitrogen alone were as good at the outset as those receiving nitrate of 
soda and muriate of potash. In nearly every case in which comparison is possible 
between potash or lime treated plots and those treated with nitrogen alone or in 
combination, nitrogen stands out as the element most needed, the one from the 
application of which the greatest response is obtained. . The fact that in most 
cases the application of nitrogen alone resulted in yields exceeding those afforded 
by potash or lime is further evidence that there was an ample supply of these 
two elements in the soil for larger crop production, that they were present in an 
available form and that they were not the real limiting factors. Theoretically 
potassium and calcium are to be considered as possible limiting factors just as 
nitrogen or iron or phosphorus or sulfur. Here and there is to be found evidence 
that occasionally they actually are not present in an available form and in 
quantities sufficient for the trees' requirements, but in the great majority of 
cases there is no occasion to supplement the supply already present in the soil. 

3. Certain elements, such as copper, arsenic and lead, are occasionally 
found in plant tissues and when present in considerable amounts they 
have toxic effects. However, their presence is the result of spray applica- 



202 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 66. — Influence of Potash-carrying Fertilizers upon Fruit Yields 



Investigator 



State 



Crop 



Fertilizer 



Yield 



Yield of 
check 



Gain, per 
cent. 



Alderman 2 . . . . 
Alderman 2 . . . . 
Alderman 2 . . . . 

Mc Cue 13 ' 

Mc Cue 1 " 

Mc Cue 131 

Gladwin 74 

Gladwin 74 

Gladwin 74 

Gladwin 74 

Ballou 9 

Ballou 9 

Hedrick, et al™ 
Hedrick, et al» 6 

Reimer 154 

Reimer 154 

Reimer 154 

Reimer 154 

Collison 30 

Collison 30 

Collison 31 ) 

Collison 3 " 

Collison 30 

Collison 30 

Chandler 25 . . . 

Brown 20 

Franklin 08 . . . 
Munson 137 . . . 
Munson 137 . . . . 

Stewart 178 

Stewart 178 

Stewart 178 

Stewart 178 

Stewart 178 

Stewart 178 

Stewart 178 

Stewart 178 



West Virginia 
West Virginia 
West Virginia 
Delaware 
Delaware 
Delaware 
New York 

New York 
New York 

New York 

Ohio 

Ohio 

New York 

New York 

Oregon 

Oregon 

Oregon 

Oregon 

New York 

New York 

New York 

New York 

New York 

New York 

Missouri 

Oregon 

Massachusetts 

Maine 

Maine 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 

Pennsylvania 



Peach 
Peach 
Peach 
Peach 
Peach 
Peach 
Grape 

Grape 
Grape 

Grape 

Apple 

Apple 

Apple 

Apple 

Apple 

Apple 

Peach 

Peach 

Apple 

Apple 

Cherry 

Cherry 

Grape 

Grape 

Strawberries 

Strawberries 

Cranberries 

Apples 

Apples 

Apples 

Apples 

Apples 

Apples 

Apples 

Apples 

Apples 

Apples 



K + P 

K + N 

Lime 

K 

K 

N 

K2SO4 

NaNO s + 

K2SO4 

N + K + P 

N+K+P+ 

Lime 

KC1 

NaNOs 

KC1 

KC1 + P + N 

KC1 

N 

KC1 

N 

N + P + KC1 

N + P 

N + P + KC1 

N + P 

Lime 

Lime 

KC1 

K2SO4 

K 

KC1 

K2SO4 

N + KC1 

N 

P + KC1 

P + K2SO4 

Lime 

N + KC1 

N 

Lime 



42.42 

71.93 

60.82 

764. 40 

1565. 90 

2210.80 

940. 50 

1185.50 
1230.50 

1118.00 

96.00 

315.60 

4877.00 

4823.50 

3.31 

14.50 

30.00 

42.25 

79.00 

77.10 

122. 70 

105. 90 

280. 00 

261.00 

11. 10 

222.00 

43.25 

2.60 

2.28 

318.20 

186. 20 

113. 10 

91.30 

73.70 

350.40 

236. 80 

61.00 



49.48 
49.48 
49.48 
684.30 
684.30 
684.30 
711.00 

711.00 
711.00 

711.00 

69.90 

69.90 

4375.00 

4375. 00 

2.85 

2.85 

30.80 

30.80 

76.80 

76.80 

111.60 

111.60 

220. 00 

443.00 

14.20 

230. 00 

48.18 

2.30 

2.30 

117.80 

98.00 

75.60 

93.20 

67.70 

230. 30 

208. 40 

53.80 



-14.2 
45.3 
22.9 
11.7 
129.6 
223.0 
32.3 

66.7 
73.0 

57.2 

27.2 

351.2 

11.5 

10.2 

16.1 

408.5 

-2.6 

37.2 

2.9 

0.4 

9.9 

-4.9 

27.2 

-69.7 

-21.8 

-3.5 

-10.3 

11.5 

-0.9 

170.2 

90.0 

49.6 

-2.4 

8.9 

52.1 

13.1 

13.4 



tions or unusual conditions of one kind or another and the problems 
incident to their presence are hardly to be considered as belonging in the 
field of nutrition. 

4. Two elements, phosphorus and sulfur, are found in all soils and 
in all plants. Though they are necessary for plant growth, deciduous 
fruits are able ordinarily to obtain all of them they require. However, 
their application in fertilizers is frequently warranted, mainly because 
of their indirect value to the trees through the effect they may have 
on intercrops or cover crops. Some attention is devoted to this phase 
of the orchard fertilizer problem. 

5. Two other essential elements, iron and nitrogen, though found in all 
soils, are often either deficient in quantity or present in forms unavailable 



SURPLUSES AND DEFICIENCIES 203 

to the plant. The result is arrested development or, in extreme cases, 
the appearance of pathological conditions. An excess of nitrogen 
also leads to disturbed nutritive relations and to pathological symptoms. 
Considerable attention has already been devoted to the question of iron 
deficiencies and to methods of dealing with them. 

6. Elaborated organic compounds of many kinds have uses in growth 
processes equal in importance to those of the mineral constituents. 
Though for the most part they are synthesized within the plant, the 
materials for their manufacture are water, carbon dioxide and the 
nutrients just mentioned. 

It is therefore evident that the question of fertilizers for deciduous 
fruits, in so far as such fertilizers serve more or less directly as nutrients 
for the plant, centers largely around the proper use of nitrogen. This is 
far from stating that fertilizers other than those carrying nitrogen are 
never of direct nutrient value. For instance, work with grapes and 
strawberries 25 suggests strongly that sulfur-carrying fertilizers in the one 
case and phosphorus-carrying compounds in the other supplied the plants 
directly with these nutrients, though it is possible that certain of their 
indirect influences may have been more important than their direct 
effects. Furthermore, there is reason to believe that many of the results 
obtained from the use of phosphorus-, potassium- and calcium-carrying 
fertilizers on deciduous fruits of different kinds and generally attributed 
to their direct nutrient value have in reality been due to their functioning 
in other ways. These statements are not made to minimize the possible 
effects or uses of fertilizing elements other than nitrogen. That they 
often are of value in the orchard there is no doubt. The point is that 
nitrogenous fertilizers act more or less directly as nutrient-carrying 
substances; others act rather indirectly through correction of unfavorable 
soil conditions or by protecting the orchard plants from harmful sub- 
stances or only indirectly as nutrients through assisting the growth of 
intercrops or cover crops. Clear differentiation between these different 
modes of operation is important, for only when there is a clear conception 
of how a fertilizer works can it be used intelligently and with certainty 
as to results. 



CHAPTER XII 
THE APPLICATION OF NITROGEN -CARRYING FERTILIZERS 



The general purpose of fertilizer application is to increase yields. 
In the orchard this may result from larger tree growth, from increased 
fruit bud formation, from better setting of the fruit, from the production 
of fruit of larger size, or from a combination of two or more of these 
rather distinct responses. 

The Influence of Nitrogenous Fertilizers on Vegetative Growth. — 
An abundant supply of available nitrogen in the soil has long been 
associated, by well informed gardeners, with strong, vigorous growth. 
So well is this connection recognized that gardeners and florists generally 
have become skilled in the art of using nitrogenous fertilizers for vege- 
tables and ornamental plants. Fruit growers, however, though inclined 
to recognize the general value of such fertilizers, have, for one reason or 
another, not employed them to any considerable extent and it is not until 
recent years that much experimental evidence has been available as to 
their place in orchard practice. 

In Peaches. — Alderman 2 reported the results of a series of fertilizer 
experiments with peaches in West Virginia. The trees were growing in 
a rather thin shale loam, a soil commonly used in that section for apples 
and peaches, though it would generally be classed as rather unproductive. 
Some of his data pertaining to shoot and leaf growth are assembled in 
Table 67. They show that wherever nitrogen was used, shoot growth was 

Table 67. — Effect of Fertilization on Vegetative Growth of the Peach 

(After Alderman 2 ) 



Fertilizer treatment 



Average 
shoot 

length, 
4-year 

average 

(inches) 



Average 
leaf area, 
3-year 
average 
(square 
inches) 



Number 
leaves 

per tree, 
3-year 

average 



Leaf area 

per tree, 

3-year 

average 

(square 

feet) 



Per cent. 

of fruit 

buds, 

4-year 

average 



Nitrogen and phosphoric acid. 

Nitrogen and potash 

Complete fertilizer 

Potash and phosphoric acid. . . 

Check 

Complete fertilizer 

Complete with potash doubled 
Complete with potash tripled . . 
Lime 



16.10 


4.28 


25,424 


14.47 


4.26 


24,808 


15 . 00 


4.06 


23,208 


8.16 


2.63 


8,768 


7.28 


2.89 


10,596 


14.40 


4.12 


29 , 536 


15.59 


4.39 


32,368 


15.00 


4.26 


22,648 


7.84 


3.26 


14,172 



755.6 
734.4 
654.3 
160.1 
212.6 
845.0 
986.7 
670.0 
320.8 



80.6 
75.5 
74.0 
58.0 
57.9 
76.6 
75.2 
76.2 
64.4 



204 



THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 205 

practically doubled; this increased shoot growth was accompanied by a 
corresponding increase in leaf number. Furthermore there was a great 
gain in leaf size; this increase coupled with the greater number of leaves 
multiplied the total leaf area by three or four. In commenting on this 
effect of nitrogen, Alderman 2 remarks: " . . . for every foot of bearing 
surface on the check tree the fertilized tree carried over 2^ feet of wood 
upon which fruit might be borne. This difference in size has been increas- 
ing so that the ratio would be much greater in favor of the nitrogen 
fertilized trees at the present time after 4 years of treatment." Inci- 
dentally the data presented in this table verify earlier statements to the 
effect that few orchards require potash, phosphoric acid or lime. 

In Apples. — Lewis and Allen 123 have reported practically the same 
influence on the shoot growth and foliage of apple trees in the Hood River 
valley, Ore., when nitrate of soda was applied to bearing apple trees in a 
rather weakened condition. They observed an even more striking change 
in the color of the foliage, which was pale yellowish green in the check 
plots and dark rich green in those that were fertilized. Still another 
effect noted many times is delayed leaf fall. This delay may vary from 
a few days to several weeks. Since the leaves late in the season can 
build elaborated foods for winter storage and spring utilization, this 
delayed maturity may bring about an accumulation of materials which 
might promote greater vegetative growth the following season and main- 
tain the tree in a more vigorous condition. At the same time, however, 
danger from sharp fall frosts or early freezes is increased, especially if 
applications are heavy enough to force the formation of new vegetative 
tissues late in the season. Consequently considerable caution should be 
exercised to apply nitrogen so as to postpone leaf fall but not materially 
to delay maturity of wood. 

In Strawberries. — Chandler 25 reports that nitrogen in either nitrate 
of soda or dried blood applied to strawberry plants in the spring before 
the crop is harvested causes excessive leaf growth and that when the 
latter material is applied even a year before the crop is to be harvested 
it causes considerably increased vegetative growth. This excessive 
leaf growth was found to be associated with decreased fruit production. 

Negative Results. Nitrogen Not a Limiting Factor. — On the other 
hand, Hedrick and Anthony 96 in reporting the results of 20 years of 
experimentation with fertilizers in apple orchards in New York state: 
" . . . heavy applications of nitrogen in a complete fertilizer and in ma- 
nure have not increased tree growth. " The results obtained by Stewart 178 
in Pennsylvania from the use of nitrogen-carrying fertilizers in bearing 
apple orchards are for the most part in accord with those of Lewis and 
Allen; at least most of his applications of nitrogenous fertilizers resulted 
in increased vegetative growth. However, some of these increases 
were comparatively small and there were a few instances in which no 



206 



FUNDAMENTALS OF FRUIT PRODUCTION 






increase was obtained. Gourley 79 found substantially the same general 
condition in his experimental plots in New Hampshire — particularly 
during the early years of the experimental treatments. Table 68 
assembled from data presented by him and some of his associates, 8 
recapitulating the first 5-years' results, explains some of the preceding 
statements that at first appear more or less conflicting. This table 
shows practically no increased vegetative growth accompanying the 
use of fertilizers, as compared with plots under clean cultivation or plots 
growing annual cover crops, even though one of the fertilizers contained 

Table 68. — Response in Vegetative Growth from Fertilizer Applications 

(After Gourley 79 ) 



Treatment 



Nitrates 








in soil in 


Yield of 


Shoot 


Size of 


parts per 


fruit, 5- 


growth, 


fruit, 4- 


million, 


year 


4-year 


year 


4-year 


average 


average 


average 


average 









Leaf 
area, 
1913 



Fresh 

leaf 

weight, 

1913 



Sod 

Cultivation every odd year 

Cultivation every even year 

Clean culture 

Cultivation and cover crop 

Cultivation, cover crop and complete 

fertilizer. 

Cultivation, cover crop and complete 

fertilizer 

Cultivation, cover crop and excess 

P 2 6 

Cultivation, cover crop and excess N. 
Cultivation, cover crop and excess 

K 2 



3.18 



17.40 
33.91 



100 


100 


100 


132 


140 


168 


176 


163 


165 


213 


190 


142 


216 


212 


135 


191 


222 


165 


195 


198 


155 


166 


200 


168 


163 


217 


196 


161 


202 


206 



100 
107 
113 
119 

124 

129 

126 

126 
125 
131 



100 
111 
117 
123 
123 

135 

131 

131 
128 
134 



relatively large amounts of nitrogen. However, soil cultivation, 
particularly when coupled with cover crops, made available to the 
plants an abundant supply of nitrogen — a supply that obviously was 
present in the sod land, but unavailable. This abundant supply met 
the trees' nutritive requirements and the surplus resulting from appli- 
cations of nitrate did not effect any consistently increased growth. 
In a report on the same series of experiments 5 years later Gourley 80 
states that though there was no special or marked increase in yield in 
the fertilized plots over those not receiving fertilizer "the orchard is 
developing in that direction." In other words, the period of maximum 
production without applications of nitrogenous fertilizers had been 
reached. This period might last for a number of years, or be of short 
duration; in either case greater and greater increases in vegetative 
growth and fruit production could be expected from proper fertiliza- 
tion. As trees increase in age and size they require larger amounts of 



THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 207 

nutrients and with the actual reduction in the total nitrogen supply of 
cultivated soils taking place each year it is easy to see how the margin of 
safety may disappear entirely. Increased vegetative growth follows 
the application of nitrogen-carrying fertilizers only when the supply 
of available nitrates in the soil is less than the plant must have for its 
best growth and there is a limit to what the plant can use. Within 
limits, surplus amounts of available nitrogen, like surplus amounts of 
available potassium or calcium or other materials, are simply tolerated. 
Analyses are not at hand showing the exact amounts of available nitrates 
in the West Virginia and Oregon soils to which reference has just been 
made, but it may be presumed that they contained very small amounts 
or amounts smaller than those required by the trees for maximum 
growth and production. 

Many orchards will not respond to nitrogenous fertilizers because 
the soils and the methods of soil management are of such a character 
that nitrogen is not a limiting factor. On the other hand experience 
shows that there are many orchards in which nitrogen is a limiting factor 
and in which, consequently, nitrogen-carrying fertilizers can be used 
profitably. To conclude from one experiment or a series of experiments 
giving negative results that orchard fertilization in general is not needed 
or that it does not pay is as erroneous as it is to conclude from striking 
returns on a nitrate deficient soil that orchards generally should be 
regularly fertilized with that element. Statements that have been made 
give some idea of the symptoms of nitrogen starvation. Short, slender 
shoot growth and small pale leaves are perhaps the most frequent indices 
of this condition, though there are many others. However, some of 
these symptoms likewise characterize injuries resulting from deficient 
water supply, borer attack or other troubles and care should be exercised 
to identify the real cause or causes of the trouble before deciding upon 
fertilization of any considerable area. 

A given supply of available nitrogen in the soil though entirely ade- 
quate for the requirements of one fruit crop may not prove sufficient for 
the best growth of another. Thus Chandler 27 has found that in a certain 
clay loam in New York applications of nitrogen-carrying fertilizers 
resulted in greatly increased shoot and leaf growth in gooseberries and 
red raspberries, though currants and black raspberries showed but little 
response. Reimer 154 reports that in the Rogue River of southern Oregon 
the Yellow Newton apple does not respond to fertilizer applications so 
readily as Esopus (Spitzenburg). Much yet remains to be done toward 
determining the actual total yearly nitrate requirements of different 
fruit crops and also their varying requirements from season to season 
with increasing age. 

Influence of Nitrogen On Blossom Bud Formation. — It is not the 
intention at this point to discuss in detail the many factors influencing 



208 FUNDAMENTALS OF FRUIT PRODUCTION 

blossom bud formation. It is generally conceded, however, that fruit 
bud initiation is in a way a response to nutritive conditions within the 
plant and it has been shown that these nutritive conditions are modified 
by the nature of the soil solution. At least theoretically, then, it should 
be possible to influence fruit bud formation through the use of fertilizers. 

In Peaches. — In a preceding paragraph Alderman 2 is quoted as report- 
ing that in his fertilizer experiments with peaches in West Virginia the 
application of nitrogen-carrying fertilizers resulted in more than double 
the shoot growth and hence double the amount of possible fruit-bearing 
surface. Data on fruit bud formation on these shoots are presented in 
the last column of Table 67. If these figures for numbers of fruit buds 
per unit of shoot length were plotted, the curve would take the same general 
direction as one for figures on total shoot length, though the two would 
not be exactly parallel. In commenting on these data Alderman 2 says: 
the "table. . . shows during the first 3 years a uniformly high percentage 
of fruit buds formed on the nitrogen-fed plots and a correspondingly low 
percentage in plots 4, 5 and 9 (those receiving nothing, potash and 
phosphoric acid or lime only). By 100 per cent, set of buds we mean that 
practically all the new growth is filled with double buds from base to tip 
. . . while a 50 per cent, set would indicate that buds were found over 
only about one-half the twig and were single in many cases." 

In Apples. — The situation is somewhat more complicated in fruits 
like the apple that bear mainly upon spurs. However, Roberts 159 has 
reported that there is a distinct correlation between the annual increase 
in length of spurs and their blossom bud formation. Both those spurs 
making a very short and those making a very long annual growth did 
not form many fruit buds, but, on the other hand, those that made a 
medium growth were highly fruitful. Length was in turn correlated 
directly with number of leaves and total leaf area and within certain 
limits {i.e., for the shorter spurs) there was also a correlation between 
spur length and average leaf area. Experiments on the influence of nitrog- 
enous fertilizers on spur length are reported by Roberts 159 as follows: "In 
1918 the difference in spur growth of non-bearing Wealthy was as follows: 
check trees 4.89 mm.; nitrate of soda 11.98. In 1919, when there 
was a larger growth on checks than usual, less difference was also noted. 
The figures for different trees than those used in 1918 are: check 7.41; 
nitrate 9.25." In general the influence of the nitrate was to increase 
the length of the spurs and consequently leaf numbers and total leaf 
areas. In the trees with spurs too short for fruit bud formation the effect 
would be to encourage that process; in those trees with spurs averaging 
just long enough or a little too long for maximum fruit format ion the effect 
would be to discourage it. Roberts 159 also points out certain correlations 
between the amount of shoot growth and the number and character of 
fruit spurs. This suggests a further indirect correlation between fertilizer 



THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 209 

applications and fruit bud formation, for the amount of shoot growth is 
greatly influenced by the available nitrate supply. The work of Hooker 100 
and others showing the importance of the synthesis and storage of organic 
compounds in late summer and fall in determining the amount and char- 
acter of growth early the next season suggests still further indirect correla- 
tions — correlations no less important, though less easily recognized, than 
those first mentioned. 

Influence of Nitrogen on the Setting of Fruit. — The influence of 
nitrogenous fertilizers on shoot and leaf growth and on the formation 
of fruit buds is not less striking than their effect on the setting of fruit, 
especially in rather weak trees that still bloom heavily. This is well 
brought out by the data presented in Table 69, for apple trees in the Hood 
River valley. 

Table 69. — Influence of Nitrate of Soda Applications upon Set of Fruit in 
Two Hood River (Oregon) Apple Orchards 

(After Lewis and Allen 123 ) 





Number of 


Percentage 


Percentage 


Average 


Treatment 


blossoming 


of fruit set 


of fruit set 


yield per tree 




spurs 


June 4 


Sept. 30 


(bushels) 


First orchard: 










Check (unfertilized) 


483 


35.3 


16.4 


3.75 


Fertilized with nitrate. . . 


542 


68.0 


30.7 


21.50 


Second orchard: 










Check (unfertilized) 


386 


9.0 


4.6 


1.33 


Fertilized with nitrate . . . 


620 


58 . 


15.1 


9.50 



The setting of fruit in the fertilized plots ranged from 100 to 300 per 
cent, higher than that in the check plots. Furthermore this influence 
was evident right after blossoming, certainly not later than the time of 
the so-called June drop. This was only a very short time after applica- 
tion and shows the prompt response obtained from such a quickly avail- 
able fertilizer. Similar results have attended the spring use of nitrate 
of soda in many other experiments with apples and pears. Indeed so well 
is the use of this fertilizer gaining recognition for this purpose that large 
quantities are now used in commercial orchards to deal with many of the 
difficulties that formerly were considered pollination problems. There 
are few data showing the influence of quickly available nitrogenous 
fertilizers on the set of other deciduous fruits, such as peaches, cherries, 
apricots and grapes. In view of their known influence in apples and 
pears this subject demands careful investigation. 

Influence of Nitrogen on Size of Fruit. — Since the size the fruit 
attains is an expression of the plant's vegetative activities it may be 
supposed that the factors or treatments leading to an increased shoot 



14 



210 



FUNDAMENTALS OF FRUIT PRODUCTION 



and leaf development will likewise lead to increased size of fruit. This 
expectation is justified by the results of many field trials with orchard 
fertilizers. Representative of many data that might be introduced 
are those presented in Table 70 for apples. In terms of percentages, 
the increase in size there reported amounts to 25 or over. 

Table 70. — Size of Apples as Influenced by Nitrate Applications 

(After Lewis and Allen 123 ) 





Per cent, grading 


Treatment 


175 to 150 per 
bushel 


138 to 112 per 
bushel 


100 per bushel 
and larger 


Check (no fertilizer) 

Nitrate of soda 


22.09 

2.28 


39.76 
26.91 


38.15 
70.76 











Pears from nitrate fertilized trees in the Rogue River valley have 
been reported to average about 178 to the box, while those from unfertil- 

110 

100 
90 
80 
10 
60 
50 
40 
30 

eo 

10 


10 

20 

2>0 

40 

Fig. 25. — Response of apple trees to fertilizer treatments, showing increases or decreases 
in yield, fruit setting and fruit coloration accompanying increased shoot growth. (Plotted 
from data given by Stewart. 178 ) 

ized plots averaged 225. 154 The graphs in Figs. 25 and 26 indicate in a 
general way the observations of Stewart in Pennsylvania and Alderman in 































































































































































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THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 211 



Virginia on the influence of fertilizer treatments on fruit size, especially 
as increases in size are correlated with increased or decreased vegetative 
growth and with increased or decreased yield. In some of the cases 
reported by Stewart, but not shown in the graphs, fertilizer applications 
were accompanied by decreased size of fruit. In commenting on his 
data Stewart 178 says: "In the 120 
matter of fruit size, some benefits 
are indicated . . . but they have 
proved less as a rule than is com- 
monly supposed. Manure has 
naturally been most consistent in 
increasing the average size of the 
fruit, probably chiefly on account 
of its mulching effect . . .in 
general we believe that the plant 
food influence will always be sec- 
ondary to moisture conservation 
and proper thinning, wherever 
greater fruit size is desired." 
Alderman 2 in his fertilizer work 
with peaches found but little in- 
crease in size from the use of 
fertilizers, nitrogen in combination 
with potash showing slight gains. 
At the Missouri Station it was 
found that in some cases the fer- 
tilization of peaches with nitrogen 
was attended by a marked decrease 
in size of fruit, this decrease some- 
times amounting to as much as 40 
per cent. 202 



no 



100 



90 



80 



10 



GO 



50 



40 



30 



20 











cfc 


GROWTH— 












f 














v 




1 


>*.„ 








I 


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Sg# 


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r 








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?0 

Fig. 26. — Response of peach trees to 
fertilizer treatments, showing increases or 
decreases in yield and fruit setting accom- 
panying increased shoot growth. (Plotted 
from data given by Stewart. 178 ) 



The explanation of the frequent failure of the fruit from fertilized 
trees to show an increase in size over that from unfertilized trees and of 
the occasional decreases in size lies in the increased wood growth and 
leaf area of the plants and consequently in their increased demand for 
water. As this increase in leaf surface may sometimes amount to over 
100 per cent, it is easy to understand how water may become a limiting 
factor. Especially is this true when it is remembered that the osmotic 
concentration of the leaves is greater than that of the developing or 
maturing fruits and hence in times of stress the fruits may actually lose 
water to the leaves which supplies their transpiration requirements 
and keeps them turgid. 26 This, however, is an indirect effect of nitrog- 
enous fertilizers on size of fruit, occasionally important in orchard 
practice and suggesting that increased attention should be given to 



212 FUNDAMENTALS OF FRUIT PRODUCTION 

meeting the trees' requirements for moisture when nitrogenous fertilizers 
are used. It also raises a series of interesting and important, but wholly- 
unanswered, questions as to the relative influence different fertilizers may 
have on different parts of the tree — for example, roots, leaves, fruit. It 
is clear that, at present, there are no means of increasing the size of fruit 
directly through the use of any particular fertilizer. Fertilizers can lead 
to the production of larger fruit only as they lead to increased vegetative 
growth and the consequently increased amounts of manufactured foods 
and as they lead to a greater extension of the root system and to a conse- 
quently greater intake of water or in still other indirect ways. 

Influence of Nitrogen on Color of Fruit. — There has been much dis- 
cussion in pomological literature concerning the use of fertilizers for 
aiding the coloration of fruits and applications of potash and phosphoric 
acid have been rather generally recommended for this purpose. Hedrick 
was one of the first to submit experimental data bearing on this question. 
After a 10-year trial with several varieties in an old New York apple 
orchard growing in a rather heavy clay he concluded that no influence 
on color of fruit could be ascribed to the potash or phosphoric acid 
which had been used. 9 " Stewart 178 in summarizing the results of his 
work with apples in Pennsylvania says: "None of the fertilizer treat- 
ments has resulted in any marked improvement in color. Slight 
and irregular benefits are shown by potash and by some of the phosphate 
applications, but nothing of any importance ..." Some of the graphs 
in Figs. 25 and 26, plotted from data presented by Stewart, furnish clear 
evidence in support of his conclusions. Alderman 2 reports a reduction of 
the red color in peaches accompanying the use of nitrogenous fertilizers 
and ascribes it to late maturity and to increased density of the foliage. 
Conversely, some slight increases in color from the use of potash or phos- 
phoric acid he ascribes to the slight checking effect these materials some- 
times have on vegetative growth. It is significant that the curves 
representing average influence of fertilizers on color are almost exactly 
the reverse of those representing their influence on vegetative growth. 
In other words, the two phenomena, those of color formation and new 
vegetative growth, are negatively correlated. 

influence of Nitrogen on Yield. — In general the tendency of nitrog- 
enous fertilizers is to increase vegetative growth, promote the formation 
of fruit buds, increase the percentage of flowers setting fruit and lead 
to larger size in the individual fruits. It is inevitable therefore that their 
general influence must be greatly to increase yields. Many data might 
be presented in support of this general conclusion. Those given in 
Tables 71 and 72 represent some of the more striking results that have 
been obtained; these, however, have been duplicated in orchards in 
many parts of the country. Table 73 is particularly interesting as 
emphasizing the importance of nitrogen compared with the other nutrient 



THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 213 

elements, in increasing yields. Perhaps it should be noted that the trees 
in both of these orchards were in a rather weak vegetative condition 
before fertilizers were applied. 

Table 71. — Influence of Quickly Available Nitrogenous Fertilizers on 
Yield of Apples in the Hood River Valley 
(After Lewis and Allen 123 ) 
Treatment 



Check (no fertilizer) , 
Nitrate of soda 



Average Yield per Tree 
(in Loose Boxes) 

0.90 
10.01 



In contrast to such striking results from the use of fertilizers it 
should be mentioned that nitrogen, alone and in combination with other 
nutrients, has been applied to many orchards without resulting in materi- 
ally increased yields. Thus Hedrick and Anthony 96 summarize the 
results of a 20-years' experiment in a New York orchard as follows: 
"Adding acid phosphate at the rate of 340 pounds per acre per year has 
not given a noticeable increase in yield. The addition of 196 pounds of 

Table 72. — Average Annual Results from Orchard Fertilizers in Ohio 

(After Ballon*) 





Average 

yield 
per tree 
(pounds) 


Average 


Value of 


Net 


Treatment 


acre 
(barrels) 


increase 
per acre 


increase 
per acre 


Nitrate of soda 5 pounds 


315.6 


67.7 


$169.25 


$163.25 


Nitrate of soda 5 pounds, acid phos- 










phate 5 pounds, muriate of potash 










2 x /2 pounds 


205.8 


37.4 


93.50 


83.50 


Tankage 5 pounds, bone 5 pounds, 










muriate of potash 5 pounds 


93.8 


6.5 


16.25 


8.25 


Nitrate of soda 5 pounds, acid phos- 










phate 5 pounds 


214.2 


39.8 


99.50 


91.50 


Muriate of potash 5 pounds 


96.0 


7.2 


18.00 


15 . 50 


Stable manure 250 pounds 


100.1 


8.3 


20.75 


20.75 




69.9 









muriate of potash to the 340 pounds of acid phosphate seems to have 
resulted in an increased yield. The annual application of 50 pounds of 
readily available nitrogen in addition to the phosphoric acid and potash 
has caused no increase in yield." Gourley, 79 ' likewise, working in New 
Hampshire with a soil of entirely different character, obtained but slightly 
increased yields from the use of nitrogen alone or in combination over 
those attending a clean cultivation-cover crop method of soil management 
without fertilization. The first of these two investigators states, how- 
ever: "An analysis of the soil before the experiment was begun shows that 
at that time there was, in the upper foot of soil, enough nitrogen (total) 



214 



FUNDAMENTALS OF FRUIT PRODUCTION 



per acre to last mature apple trees 183 years, of phosphoric acid, 295 
years, of potash, 713 years." 95 Evidently amounts of these nutrients 
sufficient for the trees' growth and production were being made available 
year after year by various natural agencies. The second of the two 
investigators, though not reporting on the total nitrogen supply of the 
soil, presents data to show that the clean cultivation-cover crop method 
of management made available each season plenty of nitrogen, though 
after some years there was some evidence that nitrogen applications in 
the near future would increase yields. 81 In the presence of abundant 
supplies additional applications gave no increased yields worth mention- 
ing. Interesting in this particular connection are data presented in 
Table 73 showing the effects of various amounts of nitrogen-carrying 
fertilizers on yield of pears. The trees were yielding well without 

Table 73. — Effects of Various Amounts of Nitrogen-carrying Fertilizers 

on Yield of Pears 

(After Reimer lbi ) 





Yield, 




Yield, 


1917 treatment 


boxes 


1918 treatment 


boxes 




per tree 




per tree 


Check 


12. 13 


Check 


15.00 




15. 12 


10 pounds nitrate of lime per tree.. . . 


18.84 


10 pounds nitrate of soda per tree 


15.45 


10 pounds nitrate of soda per tree. . .. 


18.37 


5 pounds nitrate of soda per tree 


16.53 


5 pounds nitrate of soda and 5 pounds 








superphosphate per tree 


16.63 




17.03 




17.72 


15.06 


5 pounds sulphate of ammonia 


18.23 



fertilizer applications but when small amounts of quickly available 
nitrogen were applied they at once responded, production apparently 
reaching a maximum (thinning being practiced) for the size of trees in 
question. Applications of larger amounts of fertilizer under these 
conditions resulted in no greater yield. If larger amounts are available 
they are not taken up or if taken up they are not used in increased fruit 
production. It is economical for the grower to apply only such fertilizers 
in such amounts as the tree can use with profit to himself. 

The Correlation Between Vegetative Growth and Yield. — Bearing 
directly on the question of the influence of fertilizers, particularly nitrog- 
enous fertilizers, on yield and also on that much disputed question as to 
whether vegetative growth and fruit production are antagonistic tenden- 
cies, are the graphs shown in Figs. 25 and 26, plotted from data on apple 
yields and growth as influenced by fertilizers in Pennsylvania and from 
data on peach yields and growth in West Virginia. The solid lines in 
Fig. 25 represent increase in yield (in percentages) resulting from the 
use of various fertilizer combinations. The dash-dot lines represent 



THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 215 

increases in vegetative growth, figured in the same way, length of terminal 
shoots being taken as a measure of vegetative vigor. Both lines represent 
10-year averages of a number of experiments on mature apple trees 
growing under various soil conditions. Though these curves show slight 
irregularities, those for increases in growth take the same general direc- 
tion as those for increases in yield. In other words, as vegetative growth 
has increased, yields have increased, but yields have increased much more 
rapidly than vegetative growth. This latter fact would seem to prove 
beyond all question not only that increased vegetative growth due to 
fertilization is not generally antagonistic to heavier fruit production, but 
that within limits it actually encourages heavier fruiting. Data recently 
presented for apple tree growth and yields in Delaware lead to the same 
general conclusion. 147 Graphs shown in Fig. 26, made from 4-year 
averages for increases in peach yields in West Virginia through fertiliza- 
tion, show the same relationship between vegetative growth and yield. 
Here, though yields have not quite kept pace with the increased vegeta- 
tive growth, the conclusion is obvious that in the peach increased wood 
growth is associated with increased fruit production. 

The same graphs showing the general relationship between vegetative 
growth and yield also throw some light on the way in which the fertilizers 
have increased production. Under the conditions of these tests about 
half of the increased yield was due to the greater wood growth ; in other 
words, to the effect of the fertilizer in producing additional fruit spurs and 
fruit-bud-bearing shoots. The other half of the increase was due appar- 
ently to the greater activity of the old spurs. Presumably increased 
yield was not obtained in the New York and New Hampshire experiments 
to which reference has been made because the trees' nutritive require- 
ments for new wood growth were fully met by the supply already avail- 
able in the soil and because they were already producing heavy crops. 
That decreased yield often accompanies increased vegetative growth 
following the use of nitrogenous fertilizers is indicated by results with 
strawberries in Missouri 25 and with red raspberries in New York. 27 

Influence of Nitrogen on Composition and on Season of Maturity. — 
The composition of various plant tissues, especially in so far as their 
mineral constituents are concerned, has been shown to be influenced 
considerably by the character of the soil in which they grow. Their 
composition would be expected, therefore, to show the influence of 
fertilizer application. Some interesting experimental data on this 
question have been obtained with rye, buckwheat and certain other crops. 
These crop plants were grown in what were considered normal media and 
in media possessing excessive amounts of certain nutrients. The following 
statements from the report on these experiments may be quoted here: 89 
"In general it appears as if the nutrients actually required for normal 
growth of the crops, when there are plenty of other ingredients to furnish 



216 FUNDAMENTALS OF FRUIT PRODUCTION 

the indifferent ash, need not exceed 2.0 per cent, of nitrogen, 1.5 per cent, 
of potassium oxid, and 0.5 per cent, of phosphoric oxid . . . In compar- 
ing excessive percentages with the foregoing amounts, it may be noticed 
that in certain instances . . . the percentages have increased to the 
following high magnitudes: Nitrogen, 3.96 and potassium oxide 5.56 in 
1911 in rye; and phosphoric oxide 1.36 in 1916 in buckwheat. Of course, 
these amounts are much in excess of what was necessary." The olive 
has been said to have a higher oil content when grown on a limestone 
soil. 187 Presumably fertilizing the olive orchard heavily with lima would 
have some influence in the same direction. Strawberries on nitrogen- 
fertilized plants have been found to wilt more in times of severe drought 
than those on unfertilized plants. 25 Wickson 203 states: "Puffmess of 
oranges is clearly due in some cases to excess of nitrogenous manures" 
and "the effect of excessive use of stable manures, or of other manures 
very rich in nitrogen, upon the products of the vine has been frequently 
noted as destructive to bouquet and quality." 

There are a number of indirect ways in which fertilization, particu- 
larly with nitrogenous fertilizers, influences composition. For example, 
the use of nitrate of soda in the apple orchard has been shown frequently 
to result in increased size of fruit; such differences in size are often 
correlated with differences in texture, in juiciness and in what is generally 
termed quality. These influences are not well enough understood, 
however, to make possible definite recommendations for the developing 
of certain qualities or substances, as sugar or acid or pectins, through the 
use of fertilizers. Often resistance or susceptibility to certain diseases is 
closely correlated with the chemical composition of the tissues subject to 
invasion and even a slight change in composition that might be brought 
about either directly or indirectly through the use of some fertilizer might 
be of great use in reducing injury from the invading parasite or its toxin. 

The effect of nitrogenous fertilizers on season of maturity of the 
wood has been mentioned. In the section on Temperature Relations 
it is shown that the breaking of the winter rest period in certain fruits 
is closely correlated with the time of maturing of the wood in the fall 
and in turn susceptibility to low temperatures in late winter is associated 
with the breaking of the rest period. Thus, indirectly, applications 
of nitrogen may have an important influence on certain forms of winter 
injury. Indeed the peach and some other fruits are probably grown 
sometimes under conditions where fertilization with nitrogen-carrying 
materials may be profitable for this reason if for no other. 

Application of nitrate of soda has delayed the ripening of peaches 
in West Virginia from 1 week to 10 days, the delay being greater in 
the later varieties. 2 Observations elsewhere indicate that almost any 
material carrying quickly available nitrogen has a similar influence 
on many other fruits. 



THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 217 

In a later chapter it is shown that, within certain limits, the plant 
shows very much the same response to certain kinds of pruning as it 
does to applications of nitrogen-carrying fertilizers. In other words it is 
possible within certain limits to accomplish by proper fertilization 
results comparable to those produced by pruning. This is true par- 
ticularly in the effects of these two practices on new shoot and leaf growth, 
on the better setting of fruit and on the size of fruit. Probably for 
best results there should be a judicious combination of both practices. 
For commercial production, however, it will often be found more practic- 
able to reduce the pruning to a minimum and to depend rather on 
fertilization. Fertilizers are comparatively cheap and they are quickly 
and easily applied. On the other hand pruning that is properly done 
requires considerable judgment and skill and is comparatively expensive. 
To the extent that the same results can be obtained by the two methods, 
much greater profits will be realized from the investment in fertilizers. 

Summary. — In many cases the use of quickly available nitrogenous 
fertilizers in the orchard has resulted promptly in considerably increased 
vegetative growth, the response being evident in longer shoots and in 
greater numbers of leaves that are larger in size and darker in color 
than those of unfertilized trees. For the most part these responses 
have been made by trees recently showing a lack of vegetative vigor, 
trees most likely to be found in sod land or in infertile soils. On the 
other hand there has been little evidence of increased vegetative growth 
from the application of such fertilizers to moderately rich soils in which 
the trees are already making a good growth. In many orchards, therefore 
nitrogen is not a limiting factor to growth and in those where marked 
responses are obtained from moderate applications, larger applications 
often evoke no greater response. Increased blossom bud formation 
often accompanies the increased vegetative growth that follows the 
use of nitrogenous fertilizers. Fruit setting in trees showing poor vege- 
tative vigor is greatly increased. The size of the fruit may be decreased 
or increased by the use of nitrogenous fertilzer depending on whether water 
is a limiting factor. The correlation between the amount of new vegeta- 
tive growth and fruit size is generally positive but not high. Yield, which 
is a product of fruit bud formation, fruit setting and subsequent develop- 
ment, naturally is often increased greatly by nitrogen applications. 
The development of the red color of many fruits is somewhat checked 
by the use of nitrogenous fertilizers because of the heavier shade incident 
to the increased vegetative growth. Within fairly wide limits fruit 
production is found to increase with an increase in vegetative vigor. 
The general effect of nitrogenous fertilizers is to delay maturity of 
both wood and fruit. Though some influence is shown on the composi- 
tion of the fruit, in most cases this is of secondary importance. 



CHAPTER XIII 
FERTILIZERS, OTHER THAN NITROGENOUS, IN THE ORCHARD 

The conclusion should not be drawn from the statements in pre- 
ceding chapters that in practice only nitrogenous fertilizers are of value 
in the deciduous fruit plantation. A single instance in which a favorable 
response attended the use of some other fertilizer would indicate that 
the problem should be considered from other points of view; there are 
many such instances. 

The Indirect Effects of Fertilizers. — Repeated reference has been 
made to the direct and possibly indirect effects of fertilizers on the solu- 
bility or availability of other soil ingredients, on soil reaction, or on the 
plants that constitute the mulch or the cover crop. Without doubt 
this last mentioned influence is one of the most important, especially 
in orchards not under clean cultivation. In either a sod- or grass-mulch 
or a cover-crop method of culture the vegetation produced between the 
trees is returned to the soil. Only those mineral constituents are 
returned that are obtained from the soil, but in every case there is added 
a considerable amount of organic matter which, through its effect on soil 
texture and water-holding capacity as well as through the chemical effects 
of its decomposition products, plays a very important part in the general 
aspect of productivity; with leguminous crops the nitrogen supply is 
actually augmented. Furthermore the mineral constituents may be so 
changed in form by these intercrops as to be much more available to the 
crop plants. It is generally considered that the value of these inter- 
cultures is more or less directly proportional to the amounts of vegetation 
produced. If this is the case any soil treatment or fertilizer which results 
in an increased growth of the interculture may be of indirect benefit to 
the tree. As a rule these crop plants grown between the trees are greatly 
helped by applications of nitrogen-carrying fertilizers made primarily 
for the trees' direct and immediate use. Under such circumstances the 
trees consequently receive a double benefit from their application, an 
immediate benefit from such portions as they are able to absorb before 
it leaches away or is used by the other plants and a deferred benefit 
realized only when these plants decay. 

Phosphoric Acid. — Phosphoric acid is frequently of much indirect 
benefit to orchard trees. Some measure of this influence may be obtained 
from data presented in Table 74, for an orchard under the sod-mulch 
method of management in southern Ohio. Acid phosphate alone in- 
creased the yield of mulching material more than threefold and a so- 

218 



FERTILIZERS, OTHER THAN NITROGENOUS 



219 



Table 74. — Effects of Certain Fertilizers on the Production of Mulching 

Material 
(After Ballou 9 ) 



Annual fertilizer treatment per acre 


Yield 

in 
pounds 


Kind of cover crop 




2,716 

2,884 

3,458 
840 


Red clover 


Acid phosphate 350 pounds, muriate of 


Red clover 


Acid phosphate 350 pounds, muriate of 
potash 175 pounds, nitrate of soda 350 


Timothy, red top, blue grass 




Povertv grass, weeds 







called complete fertilizer increased it over fourfold. Of equal signifi- 
cance was the change effected in the nature of the dominant vegetation. 
The unfertilized areas are reported as covered with a thin growth of 
poverty grass and weeds. 9 When these areas were fertilized with nitrate 
of soda alone or when that material was used in large quantities in com- 
bination with other fertilizers, timothy, redtop, bluegrass and orchard 
grass rapidly took the place of the weeds and poverty grass. When 
acid phosphate was used alone or in combination with potash, clover 
came in thickly and crowded out the grasses. The ground was stocked 
with all of these species before any fertilizer was applied. The effect 
of the different applications was simply to furnish one group or another 
with conditions particularly suitable for its growth while the plants of 
the other group remained small and stunted. This effect is particularly 
interesting in the case of the acid phosphate, as the clover whose develop- 
ment it made possible is a nitrogen gatherer and thus the application of 
phosphorus would result ultimately in an increased nitrogen supply for 
the trees. Probably it would not be safe to recommend generally the 
maintenance of the nitrogen supply in the orchard through the use of 
acid phosphate, but there are conditions where such a method of pro- 
cedure might be entirely practicable and there are probably many other 
orchards in which it would be desirable to supplement nitrogen-carrying 
fertilizers with those carrying phosphorus. 

Sulphur. — Similarly there is reason to believe that vegetative growth 
and production may be increased by the use of sulphur-carrying fertilizers, 
even though the soil may contain a supply of available sulphur well in 
excess of the trees' actual requirements. Elsewhere in this section it is 
stated that in certain fruit-growing sections sulphur is a limiting factor 
for the growth of leguminous intercultures, especially alfalfa. In such 
cases the judicious use of sulphur-carrying fertilizers may have a far-reach- 



220 FUNDAMENTALS OF FRUIT PRODUCTION 

ing influence on the trees, though they themselves may not be able to 
use any of it. The good results frequently obtained from the use of 
acid phosphate and credited to the influence of the phosphorus may be 
due in part to the sulphur carried by that fertilizer. 

This question of the influence of different fertilizer treatments on the 
nature of the plant population in undisturbed soil has been studied very 
carefully at the Rothamstead Experimental Station in England. Differ- 
ences are to be expected with varying soil conditions and without doubt 
the response in an orchard would be different from that in an open meadow 
such as that in which the Rothamstead investigations were conducted. 
Nevertheless the following statement from the summary of this work 
is very suggestive: 

"In the produce grown continuously without manure the average number of 
species found has been 49. Of these, 17 are grasses, four belong to the order 
Leguminosse, and 28 to other orders. The percentage, by weight, of the grasses 
has averaged about 68, that of the Leguminosse about nine, and that of species 
of other orders about 23. 

"In the produce of the plot already referred to as the most heavily manured, 
and yielding the heaviest crops, the average number of species found has been 
only 19, of which 12 to 13 are grasses, one only (or none) leguminous, and five to 
six only represent other orders; whilst the average proportions by weight have 
been — of grasses about 95 per cent., of Leguminosse less than 0.01 per cent., and 
of species representing other orders less than 5 per cent. 

"On the other hand, a plot receiving annually manures such as are of little 
avail for gramineous crops grown separately in rotation, but which favor beans 
or clover so grown, has given, on the average, 43 species. Of these, 17 in number 
are grasses, four Leguminosse, and 22 belong to other orders, but by weight, the 
percentage of grasses has averaged only 65-70, that of the Leguminosse nearly 
20, and that of species belonging to other orders less than 15. . . . 

"It is found that there is a considerable difference in the percentage of dry- 
substance in the produce, and very considerable difference in the percentage of 
mineral matter (ash) in that dry substance. There is still greater difference in 
the percentage of nitrogen in the dry matter, and, again, a greater difference still 
in the percentage of individual constituents of the ash. When, indeed, it is 
remembered that a plot may have from 20 to 50 different species growing upon 
it, each with its own peculiar habit of growth, and consequent varying range and 
power of food-collection, it will not appear surprising that different species are 
developed according to the manure employed; and, this being so, that the charac- 
ter and amount of the constituents taken up from the soil by such a mixed herb- 
age should be found much more directly dependent on the supplies of them by 
manure than is the case with a crop of a single species growing separately. 

"In further illustration it may be mentioned that, not only does the per- 
centage of nitrogen in the dry substance of the produce of the different plots 
vary considerably, but the average annual amount of it assimilated over a given 
area is more than three times as much in some cases as in others. Again, the 
percentage of potash in the dry substance is three times as much in some cases 



FERTILIZERS, OTHER THAN NITROGENOUS 221 

as in others; whilst the difference in the average annual amount of it taken up 
over a given area is more than five times as much on some plots as on others — 
dependent on the supplies of it by manure, and the consequent description of 
plants, and amount, and character, of growth induced. The percentage and 
acreage amounts of phosphoric acid also vary very strikingly; and so again it is 
with other mineral constituents, but in a less marked degree." 118 

Lime. — Calcium has been mentioned as an element practically always 
present in quantities far greater than orchard trees require. Indeed 
very large amounts are likely to lead to chlorotic conditions through mak- 
ing the soil reaction alkaline and thus rendering iron unavailable. Never- 
theless liming the soil accelerates nitrification and may thus indirectly 
help the orchard plants to obtain a larger supply of nitrogen. The 
strawberry has been mentioned particularly as a plant preferring an acid 
soil and as being actually harmed by applications of lime. Yet it is 
common experience that strawberries do exceptionally well following 
clover, though clover is very sensitive to acid soils and usually profits 
greatly from liming. In this case it is entirely practicable to apply lime 
to the clover field a year before the sod is turned under for the strawberry 
plants. The lime stimulates the growth of the clover and its effect on 
soil reaction will have largely, if not wholly, disappeared by the time the 
ground is ready for the strawberries. . Ultimately the strawberries will 
profit greatly from the lime applied to the clover that preceded them, 
though its direct application would result in serious injury. 

Illustrations might be given of other indirect influences of fertilizers, 
but enough has been said here and at other places in this section to afford 
some idea of the many ways in which they may affect orchard trees. 
Enough has been said, also, to make it clear that these indirect are often 
as important as the direct influences, for there may be no occasion to 
supply the plant with more nutrients. With our present knowledge it 
is impossible to predict with certainty all of the effects, direct and 
indirect, that any particular fertilizer will have in a given orchard. How- 
ever, this should not prevent the careful study of each situation as it 
arises. 

Plant Nutrient Carriers ; Different Forms of Fertilizers. — The neces- 
sity that the different plant nutrients be in certain forms if they are 
to be taken up by the tree has been discussed under the subjects of Solu- 
bility and Availability in Chapter VII. This does not mean, however, 
that fertilizers must contain these elements in these particular forms, 
for as soon as applied they become subject to numerous changes through 
the physical, chemical and biological factors always at work in the soil. 
Nevertheless there are certain advantages and certain disadvantages 
inherent in different fertilizers because of the form in which they carry 
the elements for which they are valued. A brief discussion of this matter 
as it applies to orchard problems is included at this point. 



222 



FUNDAMENTALS OF FRUIT PRODUCTION 



Nitrogen from Inorganic Sources. — The more common of the nitrogen- 
carrying commercial fertilizers are nitrate of soda, sulphate of ammonia 
and dried blood. Only the first of these three materials contains nitrogen 
in a form in which it is used in any considerable amounts by most plants. 
It is therefore one of the most readily available forms of nitrogen, though 
the nitrogen of the other two materials soon becomes available. The 
first two of these fertilizers are readily soluble in water and in the soil 
solution; dried blood is less soluble. This at once raises the practical 
question of loss through leaching. Some expression of the differences 
between these fertilizers in this respect as well as in their rates of avail- 
ability is obtained from an investigation on a light sandy loam in 
Florida. 31 The report on this investigation states: "For the period from 
July 13, 1911, to July 17, 1913, 41 per cent, of the sulphate of ammonia 
applied to the soil leached thru and was lost in the drainage water; 
72.5 per cent, of the nitrate of soda, and 38.3 per cent, of the dried blood 
were lost. . . . The larger loss of nitrate of soda is explained by the 
fact that this material is very readily soluble in the soil moisture and that 
the soil has very little if any power to retain or fix nitrogen in the nitrate 
form. ... In its original form the nitrogen of dried blood is not readily 
soluble in the soil water, and consequently very little is lost in the leaching 
process until nitrification occurs. In this change the organic nitrogen 
of the blood is changed first to ammonia, then to the nitrite and finally 
to the nitrate form, when it becomes as readily soluble as the nitrate of 
soda and is leached out as readily. Nitrification of the dried blood is a 
gradual process, extending over a period of time which may be of several 
weeks' duration, depending on soil conditions. Because of this, some of 
the nitrogen of dried blood, or for that matter, any similar organic mate- 
rial, will remain in the soil a considerably longer time and be available 
to the crop over a longer period than nitrate of soda. This is especially 
true where heavy rains occur after the latter has been applied to the 
soil. . . . While sulphate of ammonia is readily soluble in the soil water 
the soil has the power of fixing or absorbing at least a portion of the 
ammonia, thus preventing it from leaching away. This takes place 
through chemical means and is common to all soils. Very sandy soils 
can absorb only a small amount of ammonia; loam and clay soils are able 
to absorb much larger quantities." 

Attention may be called also to the opposite influences of nitrate of 
soda and sulphate of ammonia on soil reaction. In the former the 
nitrogen is combined with a basic and in the latter with an acid radical. 
As the nitrogen is used by the plants the soil is gradually rendered more 
basic in the first instance and more acid in the second; in the latter case 
the sulphate generally combines with calcium, resulting ultimately in a loss 
of this element from the soil through leaching. Collison 34 has found that 
in some soils this loss of calcium when sulphate of ammonia is used as a 



FERTILIZERS, OTHER THAN NITROGENOUS 223 

fertilizer amounts to over twice that taking place when nitrate of soda 
is applied. The change in soil reaction occasioned by one or two succes- 
sive applications of the same material would seldom be large enough 
to have great practical importance in the orchard, but since the effects 
are cumulative repeated applications for many years might conceivably 
result in injury to the trees. The remedy for this situation is the use first 
of the nitrate of soda and then of the sulphate of ammonia, keeping the 
soil reaction about as it is at the outset. 

Attention should be called to the inconsequential difference obtained 
in actual field trials from the use of these nitrogen-carrying fertilizers 
when nitrogen is the limiting factor and when amounts are used carrying 
approximately the same quantities of nitrogen. Nitrate of calcium 
has been employed occasionally as a fertilizer in an experimental way and 
the response has not differed materially from that to nitrate of soda. 

The different influences of these nitrogenous fertilizers on the inter- 
cultures in the orchard may be of greater significance than the differences 
in their direct influence on the trees. The acidic influence of the sulphate 
of ammonia is likely to increase gradually the growth of certain species 
like bluegrass, timothy, redtop and orchard grass and to decrease the 
growth of the clovers and certain other legumes. The basic influence of 
the nitrate of soda has the opposite effect. This is brought out strik- 
ingly by work at the Rothamstead Experimental Station 120 extending 
over a period of 30 years. Therefore if certain leguminous cover crops 
are to be grown or more especially if it is desired to keep the orchard in a 
permanent clover or alfalfa sod, some caution should be exercised in the 
use of sulphate of ammonia. Sodium, calcium or potassium nitrates could 
be used more safely. 

The results of many investigations 200 with field crops indicate that a 
given quantity of nitrogen in the form of nitrate of soda has a greater 
influence than the same amount carried in many other fertilizers. That 
is, it has more crop producing power when held in one form than in 
another. Furthermore this relative efficiency varies with many factors, 
such as the kind of crop plant and the character of the soil. Presumably 
this varying crop producing power is associated with secondary or indirect 
effects that the fertilizer or its disintegration products may have on the 
plant through their influence on soil reaction, the availability of other soil 
constituents and many other soil conditions and processes. Very little 
is known regarding the varying crop-producing value of nitrogen carried 
in different fertilizers when they are used on fruits. 

Nitrogen from Organic Sources. — A word should be said regarding the 
use of certain nitrogen-carrying organic fertilizers. Barnyard compost 
and green manuring crops have been recommended often as the best 
sources of nitrogen for the orchard. There can be no doubt but that 
they are effective fertilizers when nitrogen is a limiting factor, often 



224 FUNDAMENTALS OF FRUIT PRODUCTION 

yielding returns greater than those obtained from commercial fertilizers 
used in quantities carrying equal amounts of nitrogen. However, a part 
of their beneficial influence is without doubt due to other nutrients that 
they carry and to the effects on the physical condition of the soil. 

Thus Schreiner and Shorey, 160 in discussing the physical condition of 
the soil as affected by organic matter, state: "The organic matter may, 
and in fact generally does, play an intimate part in the behavior of the 
mineral particles, entering into chemical combination, coating them or 
cementing them together. The organic matter becomes, therefore, of 
the greatest importance in its influence on the great controlling factors in 
crop production, such as the solubility of the soil minerals, the physical 
structure of the soil granules, and the water-holding power of soils. To 
illustrate this, there was found in California a soil which could not be 
properly wetted, either by rain, irrigation, or movement of water from 
the subsoil, with the result that the land could not be used profitably 
for agriculture. On investigation it was found that this peculiarity of 
the soil was due to the organic matter, which when extracted had the prop- 
erties of a varnish, repelling water to an extreme degree. The soil, 
once freed of this ingredient, had a high water-holding power." 

Some suggestion of the many ways, direct or indirect, in which organic 
matter affects tree growth and production may be derived from the follow- 
ing statements pertaining to the rosette of pecans: "The experimental 
and other evidence indicates very strongly that pecan rosette is a sign of a 
soil deficient in humus, fertility, and moisture supply. . . . The 
constant addition of large quantities of humus-forming materials, thereby 
both bettering the physical condition of the soil and increasing its water- 
holding capacity and fertility, is absolutely necessary to produce healthy 
trees from those already diseased and to prevent the development of 
new cases of rosette. . . . some consistent and definite soil-building 
policy should be adopted in the pecan orchards of the South if rosette 
is to be overcome and healthy productive orchards maintained. The 
program of work should involve the growing of one crop, preferably a 
legume, which may be returned to the soil. ... In these experiments, 
heavy applications of stable manure, cottonseed meal and stable manure, 
and cottonseed meal alone, in connection with legumes, have proved 
highly beneficial to rosetted trees." 132 Though in cases like this it is 
impossible at present to distinguish between the influence of the nitrogen 
and that of the other components of the organic matter there is no reason 
for minimizing their combined effects or for failing to resort freely to the 
use of organic fertilizers in orchard practice where observation and experi- 
ence indicate that they may be of decided benefit. The nitrogen of 
organic fertilizers is more slowly available than that of the common 
nitrogenous commercial fertilizers and experience shows that for quick 
results the commercial sources are more satisfactory. Investigation 



FERTILIZERS, OTHER THAN NITROGENOUS 225 

shows that the nitrogen of both barnyard manure and of green manure 
crops plowed under in April or May becomes available only gradually for 
plant growth during the latter half of the growing season. 201 

Phosphorus. — Though experiments have shown little or no direct 
benefit to deciduous fruits from the application of phosphatic fertilizers 
these are often useful in stimulating the growth of intercultures or in 
promoting desirable changes and reactions in the soil. 

The leading phosphatic fertilizers available for use in the orchard are 
rock phosphate or "floats," acid phosphate or superphosphate and ground 
bone. The phosphorus in raw rock phosphate or "floats" and in ground 
bone is held in the form of tri-calcium phosphate, which is very nearly 
insoluble in water or in the soil solution and hence becomes available for 
plant growth very slowly as it is acted upon gradually by various soil 
agencies. The phosphorus of acid phosphate or superphosphate is held 
as mono-calcium phosphate, which is soluble and is the form in which 
plants are supposed to absorb most of their phosphorus. When added 
to the soil it unites with more calcium to form di-calcium or "reverted" 
phosphate which is intermediate in solubility between the mono- and 
tri-calcium compounds. Gradually this di-calcium phosphate unites 
with more calcium to form tri-calcium phosphate and it finally exists in 
the soil in the same form as in raw rock phosphate. For this reason 
"floats" or raw rock phosphate might be inferred to have equal value with 
the acid phosphate as a fertilizer. This is not the case, however, since 
the acid-treated material, being readily soluble, goes down into the soil 
and becomes fairly evenly distributed throughout the area reached by 
the roots. Furthermore, the plants are able to obtain considerable quan- 
tities before it becomes "reverted" or certainly before it is changed to 
the very nearly insoluble tri-calcium form. Mention may be made again 
of the possibility that some of the benefit from acid phosphate is due to the 
sulphur that it carries as well as to the phosphorus. Unlike nitrogen, 
phosphorus is not lost from the soil in large quantities through leaching. 
The reasons for this have been brought out in the preceding discussion. 
Some indication of the phosphorus fixing power of soil is afforded by an 
experiment with a light sandy loam in Florida in which it was found that 
at the end of four years only 0.05 per cent, of the amount applied in 
fertilizers had been lost through the drainage water. 160 

Potassium. — Though there are a number of different forms in which 
potassium may be applied, the two most common are the muriate and the 
sulphate. Where these two forms of potash have been used side by side 
in the fruit plantation the sulphate has usually, though not always, given 
more striking results. The suggestion may be repeated that when there 
is an apparent need of potash fertilizers, as indicated by a material 
response from the use of the sulphate, the possible need of sulphur be 
thoroughly investigated. In marked distinction to the case afforded by 

15 



226 FUNDAMENTALS OF FRUIT PRODUCTION 

phosphorus we have but little evidence of an indirect benefit to the trees 
through any increased growth of the intercultures resulting from the use 
of potash-carrying fertilizers. 

Sulphur. — Too little evidence on the use of sulphur-carrying fertilizers 
in the orchard is available to warrant an extended discussion of the differ- 
ent forms in which it may be applied. Evidently many different forms 
are eligible, for it has resulted in increased yields of certain orchard inter- 
cultures when used in the form of both potassium sulphate and calcium 
sulphate (gypsum) and increased grape yields have been reported from 
the use of both gypsum and flowers of sulphur. 28 Indeed it has been 
noted that alfalfa and certain other legumes have been greatly benefited 
from the sulphur contained in the lime-sulphur spray, which had 
dripped from sprayed trees or had drifted to the ground in the process 
of spraying. 

Lime. — Though calcium is one of the elements essential for the growth 
of plants, the point has been made that there are but few soils to which 
its application in fertilizers is desirable for the purpose of supplying the 
tree directly with additional amounts and though there are indirect ways 
in which it may frequently benefit orchard trees, there are indirect ways 
in which it may also injure them. The data that have been presented 
make it clear, furthermore, that the same plant may be either benefited 
or injured by liming, according to the condition of the soil. That there 
are marked differences between species — and even varieties of the same 
species — in their tolerance of lime or their tolerance of the soil basicity 
with which it is likely to be associated or in their response to lime applica- 
tions, should be emphasized. The results of work at the Rhode Island 
Experiment Station may be cited. Those results have been summarized 
as follows: "According to experiments made by the Rhode Island Agri- 
cultural Experiment Station on acid soils in that State, the plants tested 
may be classified with regard to their behavior toward lime as follows: 
Plants benefited by liming: . . . alfalfa, clover (red, white, crimson 
and alsike) . . . oats, timothy, Kentucky bluegrass, Canada pea, 
Cuthbert raspberry, gooseberry, currant (white Dutch), Orange quince, 
cherry, Burbank Japan plum, American linden . . . plants but little 
benefited by liming . . . rye, . . . Rhode Island bent, and redtop; 
plants slightly injured by liming . . . Concord grape, peach, apple, 
and pear; plants distinctly injured by liming . . . velvet bean, . . . 
blackberry, black-cap raspberry, cranberry, Norway spruce, and Amer- 
ican white birch. Other plants said to be injured are the chestnut, 
azalea, and rhododendron." 199 

Another point that may be mentioned in connection with the appli- 
cation of lime is that there is little occasion to use it in the fruit plantation 
for flocculation purposes. Soils with a texture so impervious that the 
flocculating effects of lime are needed to promote drainage and aeration 



FERTILIZERS, OTHER THAN NITROGENOUS 227 

are generally too poorly suited to fruit production, even with the aid of 
such palliative measures as liming. 

Season for Applying Fertilizers. — Comparatively few data are avail- 
able upon which to base a decision as to the best time for applying 
fertilizers of different kinds in the orchard. Without doubt many factors 
have a bearing in this connection. Among the more important may be 
mentioned: the varying states or conditions of the plant as the season 
advances, the changing nutrient value of the soil, moisture supply includ- 
ing the possibility of losses from leaching and bacterial activities of differ- 
ent kinds. It is only as these are understood and properly evaluated in 
each individual case that fertilizer applications can be timed to best 
advantage. When easily soluble nitrogenous fertilizers are required 
large amounts should not be put on in the fall, during the winter or too 
early in the spring, on account of the danger of leaching. Indeed, this 
is always a prime consideration in making nitrogen applications, though 
relatively unimportant with other fertilizers. On the other hand, 
fertilizers carrying nitrogen in organic combination must be applied 
sufficiently early to give disintegration processes time for making 
the nitrogen available to the plants before it is too late for them to 
absorb it. 

Frequent observation and experience indicate that orchard fruits 
respond very quickly to easily soluble nitrogenous fertilizers such as 
nitrate of soda and sulphate of ammonia, when these are made as growth 
is starting in the spring or later during the growing season. Thus 
Ballou 9 reports a greatly increased set of fruit in weak, devitalized apple 
trees when nitrate of soda was applied just before the opening of the 
flowers. In this case not more than 3 weeks had elapsed before it was 
clearly evident that the trees were receiving benefit from the application. 
In fact this immediate effect of quickly available nitrogen has led to the 
general practice of applying it just as growth is starting and it would 
seem that experience bears out the wisdom of so timing nitrate appli- 
cations. On the other hand, when nitrogen is needed, not so much for 
aiding the setting of fruit or perhaps for increasing the vegetative growth 
made during the early part of the current season — this latter being an 
influence which, as yet, has not been very accurately determined — but 
rather for its effects the following season, through organic products 
elaborated during the summer and fall months and stored through the 
winter, the best time for fertilizer applications may be quite different. 

Some evidence in support of this last suggestion is furnished by experi- 
mental work in England. 98 Applications of quickly available fertilizers 
to orchard trees of a number of varieties in August, supplemented by 
applications in the spring at the time of fruit setting, caused trees to bear 
annual crops. The immediate effect of the midsummer applications is 
to cause the trees to hold their foliage later in the fall, thus accumulating 



228 FUNDAMENTALS OF FRUIT PRODUCTION 

larger stores of elaborated foods and making possible the formation of 
stronger, if not more, fruit buds. 

The Relation of Seasonal Conditions to Response from Fertilizers. — 
Many features of environment may be limiting factors to growth. The 
supply of nutrients in the soil constitutes only one series or group of 
these factors. With a change in other factors it is to be expected that a 
definite balance of nutrients in the soil will limit growth in different ways 
and a corresponding variation is to be expected from the use of a par- 
ticular fertilizer on a particular soil and for a particular crop, depending 
on temperature, humidity, rainfall and other factors. Such differences 
have been studied in certain grain and forage crops. Thus applications 
of nitrogenous fertilizers to grass land give much more striking results 
when the season is comparatively dry than when it is wet. 119 Little 
is known regarding the responses of fruit trees to the same fertilizer with 
varying seasonal conditions. The great differences found in field crops, 
however, suggest that some variations may be expected. 

Summary.— Potash, phosphoric acid and lime-carrying fertilizers 
are seldom required by orchard trees, which rarely show a direct response 
to their application. However, these fertilizers often increase greatly 
the growth of intercrops or cover crops and when these are used for mulch- 
ing or green manuring purposes tree growth and production are indirectly 
increased. This indirect influence is particularly important in case the 
intercrop is a legume. Nitrate of soda, sulphate of ammonia and dried 
blood have proved the best of any of the nitrogenous fertilizers tried; 
the first two are in most common use. Sodium nitrate tends to leave the 
soil more basic in reaction and sulphate of ammonia has the opposite 
effect. These different residual effects may be of considerable importance 
under some conditions. Phosphorus is generally applied as acid phos- 
phate ; potassium, either as muriate or sulphate. Data as to the best time 
for fertilizer applications are meager. They indicate, however, that for 
increasing the setting of fruit, quickly available nitrogenous fertilizers 
should be used just as the trees are starting growth in the spring. The 
nature and relative magnitude of the response from similar fertilizer 
applications may be expected to vary considerably with different growing 
season conditions. 

Suggested Collateral Readings 

Ewert, A. J. On Bitter-Pit and the Sensitivity of Apples to Poisons. Proc. Roy. 
Soc. Victoria. 24(N.S.): 367-419. 1912. 

Kraus, E. J., and Kraybill, H. R. Vegetation and Reproduction with Special Refer- 
ence to the Tomato. Ore. Agr. Exp. Sta. Bui. 149. 1918. 

Gourley, J. H. Studies in Fruit Bud Formation. N. H. Agr. Exp. Sta. Tech. Bui. 9. 
1915. 

Wiggans, C. C. Factors Favoring and Opposing Fruitfulness in the Apple. Mo. 
Agr. Exp. Sta. Res. Bui. 31. 1918. 



NUTRITION 229 

Hooker, H. D., Jr. Seasonal Changes in the Chemical Composition of Apple Spurs. 

Mo. Agr. Exp. Sta. Res. Bui. 40. 1920. 
Hedrick, U. P. Twenty Years of Fertilizers in an Apple Orchard. N. Y. Agr. Exp. 

Sta. Bui. 460. 1920. 
Roberts, R. H. Off-year Apple Bearing. Wis. Agr. Exp. Sta. Bui. 317. 1920. 
Bedford, H. A. R., and Pickering, S. U. The Effect of Grass on Trees, etc. Pp. 

259-312. Science and Fruit Growing. London, 1919. 
Jorgensen, I., and Stiles, W. Carbon Assimilation. New Phytologist Reprint 

No. 10. London, 1917. 
Palladin, V. I. Plant Physiology, Edit, by B. E. Livingston. Chapters 3, 4, 5, 7, 8. 

Pp. 60-117 and 139-212. Phila., 1918. 
Russell, E. J. Soil Conditions and Plant Growth, Chapters 2, 6, 7. Pp. 19-51 and 

117-152. London, 1915. 

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230 FUNDAMENTALS OF FRUIT PRODUCTION 

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49. Ibid. 2:766. 

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51. Ibid. 2:772. 

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53. Ibid. 2:791. 

54. Ibid. 2:795. 

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NUTRITION 231 

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1914-1915. 



232 FUNDAMENTALS OF FRUIT PRODUCTION 

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154. Reimer, F. C. Ore. Agr. Exp. Sta. Bui. 166. 1920. 

155. Richter, L. Landw. Versuchs-Sta. 73:457-477. 1910. 

156. Rivera, V. I problemi agrari del mezzogiorno. Mem. R. Staz. Patal. Veg. 

P. 18. Rome, 1919. 

157. Roberts, I. P. Cornell Univ. Agr. Exp. Sta. Bui. 103. 1895. 

158. Roberts, R. H. Proc. Am. Soc. Hort. Sci. 14:105. 1917. 

159. Roberts, R. H. Wis. Agr. Exp. Sta. Bui. 317. 1920. 

160. Schreiner, O., and Shorey, E. C. U.S.D.A., Bur. Soils Bui. 74. 1910. 

161. Schreiner, O., and Skinner, J. J. U.S.D.A., Bur. Soils Bui. 70. 1910. 

162. Ibid. Bui. 77. 1911. 

163. Ibid. Bui. 87. 1912. 

164. Ibid. Bui. 108. 1914. 

165. Schreiner, O., Reed, H. S., and Skinner, J. J. U.S.D.A., Bur. Soils Bui. 47. 

1907. 



NUTRITION 233 

166. Shedd, O. M. Ken. Agr. Sta. Bui. 188. 1914. 

167. Shibata, K., Shibata, Y., and Kasiwagi, I. Jour. Am. Chem. Soc. 41:208. 

1919. 

168. Shull, C. A. Science. 52(N.S.):376-378. 1920. 

169. Skinner, J. J. U.S.D.A., Bur. Soils Bui. 83. 1911. 

170. Sorauer, P. Pflanzenkrankheiten. 3te. Auflage. 1:289. Berlin, 1909. 

171. Ibid. 1:292. 



172. 


Ibid. 1:297. 


173. 


Ibid. 1 :305. 


174. 


Ibid. 1:310. 


175. 


Ibid. 1:312. 


176. 


Ibid. 1:391. 


177. 


Spoehr, H. A. 


178. 


Stewart, J. P. 



Carnegie Inst, Wash. Publ. 287. 1919. 
Pa. Agr. Exp. Sta. Bui. 153. 1918. 

179. Stewart, R. 111. Agr. Exp. Sta. Bui. 227. 1920. 

180. Stewart, R. 111. Agr. Exp. Sta. Circ. 245. 1920. 

181. Stoykowitch, W. Recherches physiologiques sur la prune. Dissertation. 

Nancy, 1910. 

182. Taylor, R. H. Cal. Agr. Exp. Sta. Bui. 297. 1918. 

183. Taylor, T. C, and Nelson, J. M. Jour. Am. Chem. Soc. 42:1726-1738. 1920. 

184. Teodoresco, E. C. Ann. Sci. nat. Bot. (8) 10:141-164. 1899. 

185. Thompson, R. C. Ark. Agr. Exp. Sta. Bui. 123. 1916. 

186. Tottingham, W. E. Jour. Am. Soc. Agron. 2:1. 1919. 

187. Trabut, W. Cited by Kearney, T. H. U.S.D.A., Bur. PI. Ind. Bui. 125. 1908. 

188. Truog, E. Wis. Agr. Exp. Sta. Res. Bui. 41. 1916. 

189. Tsuji, T. La Planter. 60:413-414. 1918. 

190. Van Slyke, L. L., Taylor, O. M., and Andrews, W. H. N. Y. Agr. Exp. Sta. 

Bui. 265. 1905. 

191. Vasnievski, S. Bui. intern, acad. sci. Cracovie B. Pp. 615-686. 1917. 

192. Voechting, H., Jahrb. wiss. Bot. 25:149-208. 1893. 

193. Walster, H. L. Bot. Gaz. 69:97-125. 1920. 

194. Warren, F. G. N. J. Agr. Exp. Sta. Rept. P. 199. 1906. 

195. Webber, H. J., U.S.D.A. Yearbook. P. 193. 1894. 

196. Weber, R. Landw. Versuchs-Sta. 18:18-48. 1875. 

197. Weber, R. Forst. naturwiss. Ztschr. 1:13. 1893. 

198. Westgate, J. M. Hawaii Agr. Exp. Sta. Press Bui. 51. 1916. 

199. Wheeler, H. J. U.S.D.A. Farmers Bui. 77. 1905. 

200. Wheeler, H. J. Manures and Fertilizers. Pp. 113-124. New York, 1914. 

201. Whiting, A. L., and Schoonover., W. R. 111. Agr. Exp. Sta. Bui. 225. 1920. 

202. Whitten, J. C, and Wiggans, C. C. Mo. Agr. Sta. Buls. 131, 141, 147. 1915- 

1917. 

203. Wickson, E. J. California Fruits. P. 164. San Francisco. 1910. 

204. Wiegand, K. M. Bot. Gaz. 41:373. 1906. 

205. Wiesner, J. Die Entstehung des Chlorophylls. Vienna, 1877. 

206. Woodbury, C. G., Noyes, N. A. and Oskamp, J. Ind. Agr. Exp. Sta. Bui. 

207. 1917. 

207. Wright, W. J. Proc. Am. Soc. Hort. Sci. 11:9-14. 1912. 

208. Zaliesski, W. Die Bedingungen der Eiweissbildung den Pflanzen. P. 53 

Charkow. 1900. 

209. Zimmerman, A. Ztsch. angew. Chem. 6:426. 1893. 



SECTION III 

TEMPERATURE RELATIONS OF 
FRUIT PLANTS 

Of the four great factors of plant environment, moisture, soil, light 
and temperature, the fruit grower can modify two considerably. He 
can irrigate or drain, he can fertilize, if necessary; he can, to some extent, 
modify soil texture; light and temperature he must take as they come. 
The object of the present section is to indicate how, though temperatures 
cannot be changed, except in certain minor respects, fruit growing can be 
modified to capitalize favorable temperatures or to minimize the unfav- 
orable effects. Knowing the various effects of heat or its lack the grower 
is able to chose fruits best adapted to existing conditions, to avoid 
attempting the impossible or the very hazardous, to pick favorable 
sites and so to manipulate his plants that they will have the best possible 
adjustment to the various temperature conditions of their environment. 

Temperatures influence plants in several ways bearing directly on 
fruit growing: (1) they delimit zones beyond which the growing of specific 
fruits becomes commercially hazardous because of low winter tempera- 
tures; (2) they delimit zones beyond which the growth of certain fruits 
becomes unprofitable because of high summer temperatures; (3) they 
make certain areas unprofitable for some fruits because of low summer 
temperatures; (4) they render much good land of doubtful value for 
several fruits because of danger from spring frosts; (5) within areas ordi- 
narily safe for growing certain specific fruits an occasional deviation 
from normal may cause considerable damage; (6) some insects and 
diseases are more or less dependent on proper temperatures for their 
optimum development. 

Lest this statement should give an unpleasant connotation to tem- 
perature relations, it should be stated conversely that these very limita- 
tions predicate the presence at some places of temperatures favorable 
to fruit growing. The existence of fruit growing at all is obvious proof. 
Unfortunately attention is centered rather on the limitations, so that, 
though many unfavorable conditions are fairly closely understood, 
optimum temperatures for the various fruits are not defined so clearly. 

Schimper, 168 commenting on the difficulty of temperature investigations, 
states: the "existence of such action on vegetable organisms is less clearly 
recognizable than is that of water. We can directly observe the ingress of water 
into a plant and its egress, we can explain physiologically the effects caused by 

234 



TEMPERATURE RELATIONS OF FRUIT PLANTS 235 

these, and we can follow the transpiration current along its course, whereas the 
action of heat is carried on in the molecular region of the protoplasm beyond 
our ken, and is visible to us only in its final consequences, such as the acceleration, 
retardation or complete cessation of physiological processes. The cecological 
phenomena display similar processes. Protective adaptations against a want 
or superfluity of water are within our power of observation, those against cold 
and heat are entirely beyond them. We can directly see whether any plant 
naturally inhabits a dry or a moist station, but not whether it belongs to the 
flora of a cold or warm climate. Indeed plants from hot deserts frequently have 
a strong resemblance in habit to those of polar zones." 

The metabolism of a plant may be regarded as a complicated set of 
chemical reactions, subject to several influences. Among the factors 
governing chemical reactions and vital processes the chemist and the 
physiologist recognize temperature. There are certain limits, apparently, 
for all vital reactions, limits wide in some instances, narrow in others. 
Some plants require a relatively high temperature for setting in motion 
the processes known as growth; others will carry on similar processes 
at a lower point. One may go on at a certain temperature in a given 
plant, while another in the same plant may require more heat. At a 
low temperature a plant is said to rest; certain processes are in truth 
suspended, but others are inaugurated. Finally, there is a point so 
low that the plant cannot exist; it dies apparently from cold. On the 
other hand, all plants show their maximum growth activity within the 
limits of a comparatively small range of temperature; above these 
limits some reactions are retarded or some are so accelerated as to 
become harmful, or new injurious reactions begin and the net results that 
are recognized as growth or fruitfulness are diminished; here again the 
point is finally reached where the equilibrium of reactions is broken and 
death ensues. 

Withal, it must be considered that temperature is only one of the 
factors affecting plant growth. Even a single plant may be limited at 
various times by quite different features of its environment. 

Investigation has shown that in soy beans in Maryland growth was controlled 
during one fortnight by temperature, but in the next by the rainfall-evaporation 
ratio. 129 In Ceylon it has been found that with Agave and Furcrcea temperature 
is always the limiting factor; with Dendrocalamus sometimes it is temperature, 
sometimes water supply. In January Vitis is limited in growth by temperature 
and in July by the water supply, while with Capparis and Stiff tea the limiting 
factors are water supply during the day and temperature during the night. 181 

MacDougal 113 shows the operation of limiting factors in his study of the 
growth of tomato fruits. As the temperature of the fruits increased, growth 
progressed until the rise caused a loss of water exceeding the gain. The higher 
temperatures did not accelerate growth unless the relative humidity of the atmos- 
phere was high; a rise in temperature with decreased humidity retarded or stopped 
growth or even caused an actual diminution of volume. 



CHAPTER XIV 

GROWING SEASON TEMPERATURES 

Horticulturists, particularly in the Old World, have recognized in 
a manner the importance of growing season temperatures to fruit plants. 
Most of the efforts at precise study of this nature, however, have been 
made by those particularly interested in phenology. 

HEAT UNITS 

Various investigators have made efforts to show that, wherever 
a given plant is grown, to complete its cycle that plant requires a certain 
amount of heat. When it has received this amount of heat, whether 
in n days or n + r or n + s days, it will have completed its cycle. The 
outline of this idea was enunciated first, probably, in 1735 by Reaumur. 1 
Numerous writers since that time have attempted to refine the methods 
used in studies of this sort. Adanson, for example, recognizing that 
averages which included readings below freezing were misleading, inas- 
much as such temperatures do not reverse plant activity but merely 
suspend it, discarded all such readings. Others have assumed higher 
temperatures as the zero points for their calculations. Gasparin con- 
sidered that "effective temperatures" began at 5°C. He also considered 
a thermometer in full sunshine on sod to show the true temperature of 
the plant more nearly than one registering air temperature alone and 
that "the warmth in the sunshine is to the warmth of the air in the shade 
as though one has been transported in latitude from 3 to 6° farther 
south." 1 DeCandolle 53 believed sunlight in itself to influence vital 
processes independently of temperature, since several annuals which 
he had under observation required a greater total of heat degrees for 
flowering and for ripening in the shade than they received in full sunlight. 

The Relative Values of Different Effective Temperatures.— Most 
investigations in phenology until comparatively recent date have been 
based on the assumption that, above the basic temperature which 
initiates plant growth, each degree is of equal value with any other. 
Lately, however, the principle of Van't Hoff and Arrhenius, namely, 
"that within limits, the velocity of most chemical reactions doubles or 
somewhat more than doubles for each rise in temperature of 10°C," 
has been shown to have considerable bearing on certain processes in 
plants. As the Livingstons 109 point out, certain of the purely physical 
processes involved in growth do not follow this principle and its applica- 

236 



GROWING SEASON TEMPERATURES 



237 



tion to plants is, therefore, qualified. Fully recognizing the numerous 
limitations inherent in the data at present available, they have, never- 
theless, tentatively assigned "efficiency indices" to the various degrees of 
temperature, reproduced in part in Table 1, and applied them to the 
temperature data at various points in the United States. 

In a subsequent paper Livingston proposes a different system, based 
on Lehenbauer's studies of root growth in maize. 108 

This system differs from the others in that it is based on observed rates of 
growth and in taking cognizance of a decreased rate of growth with temperatures 
above the optimum. A comparison of the values obtained with the three 
systems is given in Table 1 . Livingston evidently regards this work only as a 
step toward further study, since he states: "... these indices are to be re- 
garded as only a first approximation and . . . much more physiological study 
will be required before they may be taken as generally applicable. In the first 
place, they are based upon tests of only a single plant species, maize, and there are 

Table 1. — A Comparison of Temperature Index Values, Starting with 40°F. 
as Unit, According to Three Systems 







System 




Temperature 








Remainder 


Exponential 


Physiological 


40 


1 


1 . 0000 


1.000 


50 


11 


1.4696 


6.333 


58 


19 


2.0000 


16.111 


68 


29 


2.9391 


46.000 


76 


37 


4.0000 


82.333 


86 


47 


5.8782 


120.000 


94 


55 


8.0000 


103.333 


99 


60 


9 . 6980 


73.111 


112 


73 


16 . 0000 


3.778 



probably other plants ... for which they are not even approximately true. 
... no doubt other phases of growth in the same plant may exhibit other 
relations between temperature and the rate of shoot elongation. Third, these 
indices refer to rates of shoot elongation, and there are many other processes 
involved in plant growth, which may require other indices for their proper inter- 
pretation in terms of temperature efficiency. Fourth, they apply strictly only 
under the moisture, light and chemical conditions that prevailed in Lehenbauer's 
experiments . . . Fifth, and finally, plants in nature are never subject to 
any temperature maintained for any considerable period of time. . . " 

Influence of Latitude on Heat Requirements. — Phenological data 
on any single fruit plant gathered over a wide area are rather scarce at 
present and those available are not altogether satisfactory. However, in 
combination with temperature data compiled by the Weather Bureau 



238 



FUNDAMENTALS OF FRUIT PRODUCTION 



some of these data are interesting, particularly since, to some extent, 
they corroborate findings of other investigators. 

In the Early Harvest Apple. — Table 2 is compiled from phenological 
data gathered by Bailey 7 and from daily normal temperatures for the 
various points, 19 except that the temperature for Columbia, Mo., is 
joined with the phenological data for Boonville, a short distance away. 
Some of the phenological data may be open to question, as, for example, 
the ripening date for Thomasville, Ga., but even with some allowance for 
errors, there is apparent a general tendency for temperature summations 
at southern points to exceed those of more northern location. Though 

Table 2. — Heat Units Calculated on Several Systems Compared with Dates 
of Blossoming and of Ripening in the Early Harvest Apple 



Locality 



Date 



Blos- 
soming 



Ripen- 
ing 



Normal 
temperature 
at average 
date of blos- 
soming, 
Fahrenheit 



Remainder 



Jan. 1 
to blos- 
soming 



Blos- 
som to 
ripening 



Total 
Jan. 1 
to ripen- 
ing 



Expo- 
nential 
Jan. 1 to 
ripening 



Physio- 
logical 
Jan. 1 to 
ripening 



Thomasville, Ga.. 

Augusta, Ga 

Atlanta, Ga 

Raleigh, N. C... 
Boonville, Mo. . . . 

Erie, Pa 

Ithaca, N. Y 

Rochester, N. Y . 



Mar. 10 


July 10 


Mar. 27 


May 30 


Apr. 8 


July 1 


Apr. 6 


July 2 


Apr. 20 


June 23 


May 23 


Aug. 18 


May 10 


July 28 


May 21 


Aug. 11 



59 
59 
59 
56 
56 
60 
55 
59 



933 


3,952 


4,945 


536 


922 


1,820 


2,742 


315 


819 


2,573 


3,392 


378 


597 


2,560 


3,157 


366 


347 


1,729 


2,076 


234 


558 


2,600 


3,158 


341 


283 


2,102 


2,385 


261 


476 


2,267 


2,743 


293 



8,383 
3,455 
5,005 
4,758 
2,979 
2,110 
3,305 
1,547 



relative positions of certain stations change with different systems of 
computing the effective temperatures, the same tendency holds through- 
out and is perhaps most evident with the physiological index summations. 
If a different zero point — say 50°F. — be assumed, the relative differences 
are not reduced materially; in fact they are rather intensified, for though 
northern points would have somewhat lower summation totals, those for 
Thomasville, Ga., would not be reduced at all, since the normal daily 
temperature for early January is 50°F. 

In the Elberta Peach. — Gould 77 reports ripening dates for the Elberta 
peach at various points in the United States. Certain of these seem near 
enough to stations for which Bigelow 19 has computed daily normal tem- 
peratures to make comparisons valid. Table 3 shows summations to the 
date of ripening and for the year at these points, with the proportion 
which they bear respectively to each other. Linsser 106 has suggested 
that this ratio should be constant, but the data here presented do not 
support his suggestion. The same tendency to greater summations in 
the south than in the north is apparent here. Waugh 203 found heat units 
for the blossoming of the "American Wild Plum" in 1898 as follows: 



GROWING SEASON TEMPERATURES 



239 



Stillwater, Okla., 967; Parry, N. J., 909; State College, Pa., 725; Burling- 
ton, Vt., 577. 

Table 3. — Heat Units to the Date of Ripening of Elberta Peach at Various 
Points and Total Heat Units for the Year 





Date of 
ripening 


Remainder 


Linsser's 
constant 


Expo- 
nential 


Locality 


To 
ripening 


For year 


index to 
ripening 


Atmore, Ala 

Plain Dealing, La 

Van Buren, Ark 

Vacaville, Cal 

Manteo, N. C 

Central Ind 

Lewiston, Idaho 

Palisades, Col 

Port Clinton, Ohio 

Freewater, Ore 

Lake region, Mich 

Ipswich, Mass 


July 11 
July 10 
July 15 
July 6 
Aug. 10 
Sept, 15 
Aug. 1 
Aug. 26 
Aug. 25 
Aug. 17 
Sept. 10 
Sept. 17 


4,654 
4,572 
3,817 
3,332 
4,911 
4,090 
3,006 
4,483 
3,639 
3,622 
3,483 
3,880 


9,540 
8,143 
8,006 
7,478 
8,475 
5,346 
5,260 
6,001 
5,170 
5,488 
4,292 
4,669 


48*8 
56.1 
47.7 
44.6 
57.9 
76.5 
57.1 
74.7 
70.4 
66.2 
81.1 
83.1 


522.9 
519.2 
432.6 

562.6 
499.4 
334.2 
500.0 
392.8 
403.4 
374.1 
418.2 



In Chestnut Blight. — Stevens has made an interesting application of these 
various constants to studies of the growth of the chestnut blight fungus. Assum- 
ing 45°F. as the lowest effective temperature, he compares the summations of 
temperatures above that point at various localities with the observed growth of 
the blight cankers and finds that "the temperature summation falls off somewhat 
more rapidly northward than does the amount of growth." In a later paper he 
reports that the summations on the "Physiological basis" do not fit the observed 
growth so well as the summations of remainder or exponential indices. 186 ' 187 

Variations in Heat Requirements from Season to Season. — Sand- 
sten 166 made a study of heat units accumulating at blossom time for the 
apple and plum during several seasons at Madison, Wis. As appears from 
Table 4, composed of items taken from his data, he found considerable 
variation from year to year and from variety to variety. Combining 

Table 4. — Number of Positive Temperature Units (above 32°F.) Received 
Each Year from Jan. 1 to the Date of First Bloom 



Variety 


1902 


1903 


1904 


1905 


Wealthv 


810.5 
837.0 
837.0 
785.0 
785.0 


837.5 
810.5 
928.0 
837.5 
810.5 


752.0 
727.0 
752.5 
707.0 
752.5 


690.0 


Borovinka 

Charlamoff 

Hibernal 

Grimes 


599.0 
713.0 
599.0 
652 







240 



FUNDAMENTALS OF FRUIT PRODUCTION 



with these figures the total heat units for the last 6 months of the pre- 
vious growing season he secured a closer approach to uniformity as ex- 
pressed in percentage of the smallest yearly total to the greatest yearly 
totals for any variety (see Table 5). Sandsten interprets his data as 
showing that other factors besides the heat units from Jan. 1 have a 

Table 5. — Number of Positive Temperature Units (above 32°F.) Received 
From Preceding July 1 to Date of First Bloom 



Variety 


1901-1902 


- 

1902-1903 


1903-1904 


1904-1905 


Wealthy 


5,106.5 
5,133.5 
5,133.5 
5,081.5 
5,081.5 


4,827.5 
4,801.5 
4,918.5 
4,827.5 
4,801.0 


4,601.5 
4,576.0 
4,601.5 
4,556.0 
4,601.5 


48,01.5 


Borovinka 

Charlamoff 

Hibernal 


47,10.5 
48,24.5 
47,10.5 


Grimes 


47,63.5 



bearing on the time of flowering and enumerates as possible factors the 
stage of advancement of the buds at the time of growth cessation in the 
fall, the size of the crop borne in the previous year, "soil conditions and 
the amount of plant food present in the soil; and fifth, the individual 
characteristics and state of health of the tree or plant." General observa- 
tion on peach trees shows a sequence in opening blossoms corresponding 
to the stage of advancement of these buds in the fall, the difference in 
time of flowering on the same branch amounting sometimes to several 
days, which would make a difference occasionally of 50 units or more on 
the Fahrenheit scale. Magness makes an interesting suggestion in this 
connection which is referred to under Fruit Bud Formation. 

Seeley 176 applied the method of temperature summations to the Late 
Crawford peach, as recorded in the Mikesell data for Wauseon, Ohio. 
His summary of results, shown in Table 6, indicates no close agreement 
from year to year for the same locality. Somewhat closer tallying was 
secured when maximum figures were used (line 4) . Seeley shows that air 
temperatures as recorded by thermometers in the conventional shelter do 
not indicate at all closely the actual temperatures of the leaves. 

Table 6. — The Least and the Greatest Temperature Summations in the Life 
Phase of the Late Crawford Peach 

(After Seeley 176 ) 



Summation 


Jan. 1 to 
blossoming 


Blossoming 
to ripening 


Jan. 1 to 
ripening 


Ripening to 
blossoming 


Average 


Least 

Greatest 

Percentage 

Maximum (per cent.) 


183 

362 

50 

64 


2,776 

3,991 

70 

71 


3,030 

4,347 
70 
72 


486 

1,250 

38 

61 


61 
69 



GROWING SEASON TEMPERATURES 241 

Acclimatization to Varying Amounts of Heat. — It is conceivable that 
through acclimatization plants gradually may require more or less heat 
for a given function; evidence to this effect is cited by Bailey. 9 Cuttings 
of Concord grape from Maine, central New York and southern Louisiana 
planted simultaneously under uniform conditions at Ithaca, N. Y., made 
in a given time the following respective growths: 2.66 inches, 1.6 inches 
and 1.3 inches. The seed potato trade of Maine is founded on the quick- 
ened response to a given temperature by potatoes grown there. Data 
already cited in this chapter show a tendency for plants in northern 
sections to attain a given stage of development with less heat than in 
southern sections. Elsewhere it is shown that plants accommodate them- 
selves to a wide range of moisture, nutrient and light conditions; there- 
fore it is not surprising that they show a corresponding adaptation to 
various temperature conditions. 

In General. — It is possible that more detailed measurements, taken 
perhaps on a different basis than that used by climatologists, would 
secure more uniformity than the figures cited above. Temperatures 
taken in sunlight would seem to be more reliable expressions of conditions 
in buds and leaves than those taken in shade. Some writers have sug- 
gested maximum temperatures as the basis for calculations. In any case, 
however, it seems doubtful if temperature alone can be made the index 
of plant activities. 

Schimper 169 aptly points out that "different organs and functions require 
very different amounts of heat, that unfavorable temperatures cause subsequent 
inhibition, and that other factors besides heat, especially humidity, cooperate 
and intervene. We need not, then, be surprised if there is very little accord in 
phaenological observations, and that the utmost one can do is to admit their 
having a certain importance for purely descriptive geographical botany in the 
characterization of certain districts. No importance, on the other hand, need 
be assigned to the theoretical views, nor to the sum total of temperatures." 

OPTIMUM TEMPERATURES 

It is well known that some plants grow at lower temperatures than 
others. The necessity of a certain amount of heat during the growing 
season is recognized in the statement that in some regions the summers are 
too cool for certain fruits. 

Variation within the Species or Variety. — In considerable areas of 
north central Europe, peach growing is limited, not by the cold of winter 
but by the low summer temperature. The same limitation, though 
less obvious, probably applies to pears, as is indicated by the transition 
from open exposures in the south of France to the trained and sheltered 
trees in the north. Among plants of warmer climates the date palm 
shows a heat requirement that is not satisfied in all sections where the 

16 



242 FUNDAMENTALS OF FRUIT PRODUCTION 

winters are sufficiently mild. The grape is among the plants most 
frequently cited by phenological workers as showing this same exaction 
in its requirement. Variety adaptation in apples probably depends on 
growing season temperature, among other factors. In addition it seems 
rather likely that this factor is operative in another way though its 
effects necessarily are masked by their own results; low summer tem- 
perature may delay maturity to such an extent that an ensuing winter of 
medium intensity is injurious. The obvious and immediate cause of 
trouble here would be winter injury but the antecedent cause would be 
the cool summer. Much of the winter injury characteristic of parts of 
Europe seems to be involved with low summer temperatures. 

The effects of temperature alone in certain phases can be compared 
best, perhaps, in plants of the deserts, since these regions show rather 
greater uniformity in other conditions than most humid sections. In 
the date palm temperature assumes considerable importance. 

According to Swingle: 191 "The northern limit and the limit of altitude in 
northwestern Africa at which dates can be grown are set more by the deficient 
summer heat failing to ripen the fruit than by the cold in winter." Very early 
ripening dates, he reports, can be grown far to the north where the summers are 
not warm enough to ripen later varieties. Swingle confirms DeCandolle's 
calculation of 64.4°F. as the point below which no effect is produced on flowering 
or fruiting of the date palm. Affirming that under desert conditions temperature 
summations have considerable significance he states that 2000°C, using 18°C. 
as the zero point, are necessary to ripen Deglet Noor dates satisfactorily. 

Mason 123 cites Caruso as authority for the statement that 51° to 52°F. 
is zero point for the olive and adds that in California zero may be some- 
what higher, probably 55° to 56°F. He assigns a definite number of heat 
units as necessary for ripening the olive before autumn, but points out 
that in some localities with low summer temperatures and little or no 
frost in winter the fruit may remain longer on the trees. In some 
places the requisite number of heat units is not accumulated until 
December. 

The apple shows some indications of the effects of excessive summer 
heat at some points in the United States and of deficient summer heat at 
others. Along the southern limits of its successful culture there is a 
general tendency to vigorous vegetative growth with little fruit produc- 
tion and much of the fruit that is borne rots on the tree. In that period 
when apple varieties were being tested and when the varietal composition 
of the orchard was not determined by market standards of the large 
cities, the Ribston Pippin attained a much greater popularity in eastern 
Maine than in any other section of the country then growing apples. 
Other English varieties were more favorably received there than in any 
other state. Downing 56 considered that the Ribston attained far better 



GROWING SEASON TEMPERATURES 243 

quality along the Penobscot River than in the middle states. Inci- 
dentally he mentioned English gooseberries as succeeding better around 
Bangor, Maine, than elsewhere. It seems probable that the cool sum- 
mers of that section favored the best development of these fruits. 

The converse limitation is less generally understood but it is none the 
less potent. Most varieties of apple have certain heat requirements for 
the attainment of their best quality or indeed for their ripening. Cions 
of the Baldwin, favored by a succession of mild winters in Aroostook 
County, bore fruit which failed to ripen because it was arrested in its 
development by cold weather while still green. 26 Shaw 179 found marked 
differences in Ben Davis grown in various sections, indicating incomplete 
development in much of the northern apple growing section. The limits 
of successful culture of many varieties are conditioned by the minimum 
winter temperatures, thus rather obscuring the importance of summer 
heat but, as with other fruits, there seems to be some reason for consider- 
ing winter hardiness in some cases to be affected by summer temperatures. 
So far as climatological data show, the minimum winter and average 
winter temperatures for Boston, Mass., and Columbia, Mo., are almost 
identical, but their summer temperatures differ considerably. Winesap is 
considered tender and unsatisfactory in Massachusetts while in Missouri 
it is one of the best commercial varieties. Apparently the limitation is 
set by winter temperature in the Mississippi valley and by summer 
temperature, directly or indirectly, along the Atlantic seaboard. The 
northern commercial limit of York Imperial crosses the Mississippi near 
the southern Iowa border and the Atlantic coast in New Jersey. 179 Here 
again the correspondence between the northern limits east and west is 
better in summer temperatures than in those of winter. The same con- 
trol is evident with Rome Beauty. 

Shaw 179 concluded after extended study that a certain optimum 
summer temperature may be assigned to each variety of apple, ranging 
from 52°F. for Hibernal and Oldenburg to 67°F. for Terry and Yates. 
As appears from Table 7 the temperature range of the chief commercial 
varieties is somewhat more narrow. A considerable effect, however, on 
the limits of commercial cultivation of apple varieties must be assigned 
to summer temperature. 

Table 7. — Optimum Average Summer Temperatures for Leading Commercial 

Varieties 
(After Shaw 179 ) 

Baldwin 56°F. Yellow Newtown 60°F. 

Rhode Island 56 York Imperial 62 

Northern Spy 56 Grimes 62 

Wealthy 56 Stayman 63 

Jonathan 59 Winesap 64 

Delicious 59 Ben Davis 64 



244 



FUNDAMENTALS OF FRUIT PRODUCTION 



In the United States, Lippincott 107 traced isotherms for combined June, July, 
August and September temperatures and correlated them with the grapes growing 
in the zones thus marked out. Here a combined selection is exercised by summer 
and by winter temperatures and in addition, as pointed out elsewhere the summer 
temperatures doubtless have some influence on the effect of winter cold. How- 
ever, there can be no doubt that summer temperatures have a direct effect of 
their own. In favored localities in the zone with a mean of 65°F. he found 
Clinton and Delaware, with a few other varieties. In the 67°F. zone he included 
Concord and Hartford Prolific; Isabella, Diana and Rogers' Hybrids he con- 
sidered to require 70°F. Catawba, Norton's Virginia, Herbemont and Scupper- 
nong were assigned to regions with average summer temperatures of 72° or higher. 

Differences within the Variety for Separate Processes. — Different 
processes in the same plant have different optimum temperatures. 

Phytolacca decandra at Carmel, Cal., grows well but flowers only under certain 
conditions as, for example, when prostrate branches receive sufficient additional 
heat from the soil to enable them to form viable seeds, while the erect stems 
do not. 110 In connection with fruit setting it is shown that lower temperatures 
than usual convert male blossoms of the papaya into perfect flowers. Schimper 
points out the difference in the temperature curve for the two forms of gaseous 
exhange and states that assimilation occurs at lower temperatures than any 
other function. He cites evidence of assimilation in Abies excelsa and other 
plants at — 40°C. and cites Bohm as finding the optimum for the walnut at 30°C. 
No distinct respiration could be observed in Abies below — 10°C. ; this function 
increases, speaking in general terms, with the temperature until the lethal point is 
approached. Quoting Schimper 169 again: "There are, however, certain physio- 
logical processes for which not only the optima, but also the upper zeros are so 
low that, as a rule, they can take place only in winter, late autumn, or early 
spring. The category of functions that are active at low temperatures only 
includes among others the obscure processes which are fermentative in nature, 
according to Sachs' hypothesis, and which awaken into activity hibernating 
parts of plants; among such processes may be cited the conversion of starch into 
fatty acids and the reverse. . . . Lower temperatures exert a favourable influ- 
ence on the sexual organs and on the parts cecologically connected with them 
(perianths, inflorescence axes) in many parts of the temperate and frigid zones. 
The cardinal degrees for the growth — -and perhaps for the inception — of the 
primordia of flowers are often much lower than for the growth of vegetative 
shoots, so that the former are favoured by a relatively lower temperature, and the 
latter by a high temperature, during development. It is well known that 
Crocus, Hyacinthus, and other perennial herbs do not send out flowers or inflores- 
cences at a high temperature, but shoot out luxuriantly into leaf. Also in the 
forcing of fruit trees the temperature must be kept moderate before, and espe- 
cially during, the blossoming period. For the same reason many temperate 
plants seldom blossom in the tropics; for example, most of our fruit trees. . . . 
Kurz found in the mountains of Burmah that increased coolness due to increased 
altitude expedited the blossoming of temperate plants such as Rhododendron and 
Gcntiana, but delayed that of tropical ones." 



GROWING SEASON TEMPERATURES 



245 



As Schimper 171 points out, the forcing of fruit under glass is merely a 
shortening of the dormant season and the period of maturity is advanced 
only as much as the inception of growth precedes that in the open. The 
temperatures found best for the trees indoors are those they receive at 
corresponding stages out of doors in favorable regions; higher temperatures 
are not beneficial. 

Price 155 reports investigations showing certain temperatures more 
favorable to the opening of fruit buds than others. With branches of 
various fruit trees in incubators maintained at different temperatures he 
found progressive acceleration in the opening of the buds with the higher 
temperatures. Some of the data he reports are used in compiling Table 8. 



Table 8. — Influence of Temperature on Opening of Fruit Buds 



Fruit 



Date of 
beginning 



Davs to full bloom 



70°F. 



79°F. 



88°F. 



Abundance plum . . . 

Hale plum 

Luster peach 

Kieff er pear 

Oldenburg apple. . . . 
Rome Beauty apple 



Jan. 28, 1908 
Dec. 3, 1909 
Feb. 2, 1909 
Mar. 7, 1910 
Apr. 1, 1909 
Apr. 22, 1909 



10 
12 
13 
13 
12 
8 



6 
9 
9 
11 
6 



Tufts 196 reports interesting indications that very high temperatures may 
retard the ripening of fruit. "Here," he states, referring to the Winters section 
in the Sacramento valley, "... the apricot ripens some two or three weeks prior 
to the ripening of the apricot crop in the Santa Clara Valley, although apricot 
trees in the Santa Clara Valley bloom ten days earlier than they do in the Winters 
section. Undoubtedly the nearness of the ocean and the influence of the San 
Francisco Bay profoundly modify the climate of the Santa Clara Valley. The 
Apricot crop in the Winters section is entirely harvested by July 1. 

"When it comes time for the prune harvest, however, we find that the Santa 
Clara Valley is generally pretty well along — about half way through — before the 
prunes in the Sacramento Valley are ready. The only explanation we have for 
this apparent inconsistency is the fact that probably the temperatures for the 
ripening of the apricot crop are optimum in the Winters section. However, after 
the first of July the weather gets excessively warm, with the result that the prunes 
are retarded in their development, and the optimum temperatures for the develop- 
ment of the prune crop probably exist in the Santa Clara Valley during the latter 
part of the growing season." 

Schimper, 170 emphasizing that different functions require different 
temperatures, states: "the cecological optimum temperature does not 
remain constant during the whole development of a plant, at least in tern- 



246 



FUNDAMENTALS OF FRUIT PRODUCTION 



perate regions, but . . . shows a rise as development proceeds. . . . We 
learn too from the art of fruit forcing that we must regard the rise not as 
constant but as oscillating." He cites Pynaert in giving the tempera- 
tures shown in Table 9 as most favorable in forcing the peach. At two 
periods the temperature is lowered. Ward 201 in England and Schneider 172 
in northwest Europe differ somewhat in detail from this temperature 
statement; Schneider indicates a lowering of temperature at the time of 
stoning. 



Table 9. — Optimum Temperatures in Forcing the Peach 170 
(Degrees Centigrade) 



Day temperature Night temperature 



First week 

Second week .... 

Third week 

To flowering .... 
At flowering. . . . 
After flowering. . 
During stoning. . 
After stoning. . . 
At fruit ripening 



9 to 10 
10 to 12 
12 to 15 
15 to 18 

8 to 12 

15 to 18 
12 to 15 

16 to 19 
20 to 22 



5 to 7 
7 to 9 
9 to 11 

11 to 14 

6 to 10 

11 to 14 
9 to 11 

12 to 15 
15 to 17 



Variation in Quality with Amount of Summer Heat. — The fruit 
which has received the most careful study in its relation to temperature 
conditions is the grape. Blodgett, 20 writing in 1857, when grape growing 
in America was in an experimental stage, predicted very closely, from 
climatological data, the geographic distribution of the industry in the 
United States. 

Boussingault 22 early remarked on the variation in yield and quality of wine 
of a vineyard in Flanders, the variation depending on the temperature of the 
growing season, and reported data shown in Table 10. Baragiola, 13 taking succes- 
sive samples of grapes through two autumns, found a striking correspondence 
between sugar increase and temperature, regardless of the stage of ripening at 
which the low or high temperatures occurred. A brief period of warm weather 
late in the season compensates apparently to a considerable degree for earlier 
deficiencies: a brief period of cool weather at the same stage apparently goes far 
to nullify previous favorable conditions. Heat requirements for grapes during 
the growing season can be understood best from European experience since the 
climatology of this fruit has been studied most extensively there and is to a 
considerable degree free from the complication of winter temperature limitations. 
Boussingault 22 considered that the mean temperature of the growing season 
must be at least 59°F. and of the summer 65° to 67°F. to produce Vinifera grapes 
satisfactorily. In some of the equatorial table lands of South America, he 
states, where the mean temperature is 62° to 66°F. with little range, though the 



GROWING SEASON TEMPERATURES 



247 



Table 10. — Relation of Summer Temperatures to Yield and Character of 

Wine 22 





Mean temperature 


Wine, per 
acre (gallons) 


Percentage 
of alcohol 




Year 


Growing 
season, de- 
grees Centi- 
grade 


Summer, 

degrees 

Centigrade 


Beginning 
of autumn, 

degrees 
Centigrade 


Alcohol per 
acre (gallons) 


1833 
1834 
1835 
1836 
1837 


14.7 
17.3 
15.8 
15.8 
15.2 


17.3 
20.3 
19.5 
21.5 

18.7 


11.4 

17.0 
12.3 
12.2 
11.9 


311 
314 
621 
544 

184 


5.0 
11.2 

8.1 
7.1 

7.7 


11.4 
46.3 
50.0 
38.6 
14.0 



vines nourish the grapes never become thoroughly ripe and good wine cannot be 
made where the constant temperature is not at least 68°F. Besides a warm 
summer, a mild autumn free from continued low temperature is necessary. 
Some regions are assured of sufficient heat in every summer; others must have 
a summer warmer than the average to produce a satisfactory wine. Along 
the doubtful zone of grape growing the careful selection of site is emphasized. 

Variation in Season of Maturity with Amount of Summer Heat. — 

The effect of summer temperatures on the time of ripening and on keeping 
qualities is well known. The Wealthy, a fall or early winter apple in 
Minnesota, becomes a summer apple in Missouri. The Baldwin loses 
quality and becomes progressively a poorer keeper toward the south 
except at higher and cooler altitudes. Sometimes the transition is rather 
abrupt. The Dudley, a winter apple in Aroostook County, Maine, is a 
fall apple at Bangor and a summer apple farther south. 26 Apples grown 
in southern latitudes develop color over a larger part of the surface, but 
the colors are more intense in the north. 



SOIL TEMPERATURES 

That the temperature of the soil is not without influence on plant 
growth is evident from the florist's resort to bottom heat for certain 
plants and the rather definite heat requirements for the rooting of cut- 
ings. It has been shown that Opuntia versicolor can be stimulated to con- 
siderable vegetative growth despite unfavorably cool atmosphere by the 
maintenance in the soil of favorable temperatures for root growth. 30 
Lindley 104 stated that a certain variety of Nelumbium though in full vegeta- 
tive vigor was without flowers when the soil temperature was 85°F., but 
blossomed at 70 to 75°F., while another variety ceased blossoming at 
this same temperature. 

Obvious difficulties are encountered in attempting a determination 
of suitable temperatures for root growth in trees. Lindley 105 arranged 
a statement of favorable soil temperatures for various fruits, based on 



248 FUNDAMENTALS OF FRUIT PRODUCTION 

observations in sections where these fruits nourish; the growing season 
temperatures thus indicated range from 54°F. for the gooseberry, 59°F. 
for the apple, and 65°F. for the peach to 85°F. for the mango. Goff 74 
found that root growth begins very early in most fruit plants in Wisconsin, 
starting in most cases in advance of the buds. When currant buds were 
but little swollen some of the new roots were 3 inches long. Goff stated, 
however, that warmer temperatures did not accelerate root growth as 
much as might be expected from the early start. Comparison of the 
growth of young apple trees under various systems of culture, with accom- 
panying differences in soil temperature, has shown that the two systems 
inducing the greatest extremes in temperature resulted in practically 
the same growth. 142 The extremes, however, were not widely separated. 
It would seem that in some cases when a choice of stocks is possible 
the adaptability of the several stocks to soil temperatures should be 
considered, along with other factors. It appears rather illogical, for 
example, to plant prune trees on peach roots in a soil so cold that it 
would not be considered suitable for peaches. An instance of at least 
partial adaptability to soil temperatures has been reported in Baluchistan, 
where plums, peaches, etc., on Black Damask and Mazzard roots repeat- 
edly failed to thrive, though the same combinations are satisfactory 
in Great Britain. 96 Using other stocks such as Mariana, Myrobolan 
and Mahaleb, that apparently are better adapted to hot, dry soils, much 
better results were secured. 

INDIRECT TEMPERATURE EFFECTS 

Finally, another limiting effect of growing season temperatures should 
be considered, namely, that on fungous diseases. Apple scab, for example, 
has a generally northern range, suggesting adaptability to cool summers, 
while blotch is confined to sections with rather warm summers. Pear 
blight is distinctly a warm weather disease; brown rot is favored by 
high temperatures in conjunction with humidity. All these diseases take 
toll of the fruit grown where they are present; brown rot, in conjunction 
with curculio, makes plum growing a hazardous occupation in the south- 
east United States and blight practically prohibits the commercial 
production of the European pear in the southeast and in the Mississippi 
valley. 

Summary. — Functional activity and growth of any kind in a plant 
have definite temperature requirements. Within the limits between 
which the growth processes can proceed development is slowest near each 
extreme — that is, close to the lower and close to the upper limit. Growth 
is most rapid at an optimum temperature somewhere between the two 
extremes, but usually nearer the upper than the lower limit. Further- 
more the optimum for certain growth processes is quite different from 
that for others within the same plant and the extremes likewise may 



GROWING SEASON TEMPERATURES 249 

be different for different activities. Consequently it becomes extremely 
difficult, if not impossible, to assign definite values to different temperatures 
in their total growth effects, and the "heat units" necessary for com- 
pleting certain changes, or carrying the plant through certain aspects 
of its seasonal life history, vary considerably with conditions. In general 
fewer heat units are required by a given plant in northern than in southern 
latitudes. Other conditions being equally favorable, there is the best 
varietal adaptation in sections where growing season temperatures 
most nearly approach the optimum for the variety in question. The 
importance of summer growing temperatures in determining "the com- 
mercial limits of fruit varieties is underestimated. Summer temperature 
likewise exerts an important influence in determining the season of 
maturity of the fruit. Soil temperature is of possible importance in 
influencing growth and in determining the geographical range of certain 
varieties. Injurious effects of soil temperatures can be minimized 
sometimes by the use of stocks of the right kinds. Summer tempera- 
tures also have an important indirect effect on orchard plants through 
their influence on the range or activity of certain parasites. 



CHAPTER XV 

WINTER KILJJNG AND HARDINESS 

The limits to fruit growing set by low winter temperatures have been 
indicated. This limitation has been shown to be influenced more or 
less by other factors, precipitation in some cases, summer temperatures 
in others. Low winter temperatures are important, however, in other 
respects than merely marking boundaries separating a section where 
a given fruit is grown from another section where it is not. Damage 
by freezing is not confined to any one region; it is as definitely an injurious 
factor in California and Florida for tender species as it is in Montana 
or Wisconsin for the more hardy fruits. It is not confined to the border- 
lands of a fruit zone but in one way or another makes itself felt well 
within the regions adapted to fruit growing. It is not a simple matter 
of uniform, predictable reaction to a given temperature but is modified, 
intensified or palliated by varying factors and is itself probably a group 
of fatal or damaging reactions assembled for convenience or for want 
of discriminating classification under the single name of winter killing. 

DEATH FROM FREEZING 

Several explanations of the actual process of killing of tissue by low 
temperatures have been made; it seems possible that there may be more 
than one way by which the killing is brought about. Parenthetically, 
it should be stated that the original theory and the one still most fre- 
quently advanced by practical men, i.e., that death by cold is due to 
expansion accompanying freezing and a consequent rupture of the cell 
walls, is not tenable as can be proved mathematically or by microscopic 
examination. The bursting of trunks and limbs, cited to justify this 
contention, is considered later. The view held most generally by inves- 
tigators ascribes death to withdrawal of water from the cell, a process 
comparable to death by plasmolysis. 

Tissue Freezing is Accompanied by Cell Dehydration. — Numerous 
investigators have shown that ice is very rarely formed within the cell 
unless the cooling is very rapid, more rapid, in fact, than would occur in 
nature. Before freezing begins, since the cell sap contains substances 
in solution and because of capillary supercooling, most tissues must be at 
a temperature several degrees below the freezing point. The first evident 
step in the process of freezing is a contraction of the protoplasm and the 
appearance of water in the intercellular spaces where it has been forced 
or drawn from the cell. Ice formation begins at various points in the 

250 



WINTER KILLING AND HARDINESS 251 

intercellular spaces, frequently making lens-shaped masses of hexagonal 
crystals, larger at the side which draws on the greater number of cells. 
As the growing ice needles deplete the water of the intercellular spaces, 
more is drawn from the cell contents. 214 The continuance of this process, 
however, makes the sap remaining within the cells more concentrated 
and thus increases "the force with which the remaining quantities of 
water are held." 214 A still stronger force, operating as a reserve, is that 
known as molecular capillarity, holding with extreme tenacity a certain 
amount of water of imbibition. Hence, it is with increasing difficulty 
that ice formation continues and it must cease sooner or later unless the 
temperature be lowered further. Moreover, the very process of solidi- 
fication liberates a certain amount of heat. Therefore it is not surprising 
that, as the temperature falls, the ice formation for each degree becomes 
progressively less. Miiller-Thurgau found, at 4.5°C, 63.8 per cent, of 
the water of an apple frozen, while at -15.2°C. only 79.2 per cent, had 
frozen. 214 Wiegand 213 found very little ice in dormant twigs of many 
species of forest trees at 20°F. At 0°F. ice was plainly visible in buds of 
19 species out of the 27 examined; 6 of the remaining 8 showed ice, 
but in small scattered crystals, at — 15°F. These buds "all contained 
little cell-sap and small cells with rather thick walls." 

As the ice crystals increase, the cell walls collapse and become packed 
together in dense masses. Buds and bark of hardy trees show this 
condition, as do evergreen leaves, but at suitable temperatures they 
expand, draw back the water and become normal. 

Wiegand 213 reports: "The ice was found to occur always in broad prismatic 
crystals arranged perpendicular to the excreting surface; and usually formed a 
single continuous layer throughout the mesophyll of the scale or leaf, to accom- 
modate which the cells were often separated to a considerable distance. This 
ice sheet was composed of either one or two layers of the prismatic crystals, 
depending on the water content of the adjacent surfaces, and was often as thick 
as the whole normal scale. The cells surrounding the ice, having lost their water 
content, were in a more or less complete state of collapse, depending upon the re- 
sistance of the walls, and often occupied a space smaller than the ice itself. These 
cells were uninjured, however, and would resume their normal condition on 
thawing. ... In young anthers the ice often filled the entire anther cavity 
and in it the pollen grains were imbedded in a completely collapsed state." 
At temperatures between — 23.5°C. and — 18°C. in the apple and pear the 
tissue was "packed full of ice in shoot and in the mesophyll of the scales." In 
general, the species in which ice formed most readily had larger cells, a higher 
water content and a greater proportion of water to cell wall and protoplasm. 

"In the twigs," Wiegand states, "ice is also present in very cold weather, 
where it may be found in three different localities. The largest quantity occurs 
in the cortex, where the ice crystallizes in prisms arranged in single or double 
series according to the law of freezing tissues. The ice is more frequently in 
the form of a continuous ring, or really a cylinder, extending entirely around the 



252 FUNDAMENTALS OF FRUIT PRODUCTION 

twig, prying apart the cells of the cortex in which it lies. The outer cylinder 
of cortex in such twigs is completely separated from the inner layers when frozen. 
In a few species instead of the continuous layer, lens-shaped ice masses are inter- 
polated irregularly throughout the cortex. The cortical cells after the withdrawal 
of water are as completely collapsed as were those in the bud scales, but they also 
usually regain their normal condition on thawing. In the wood ice rarely forms 
in large quantities. It is usually confined to small masses in the vessels them- 
selves, or, according to some authors, sometimes extends in radial plates in the 
pith rays. In sectioning twigs I, myself, have never seen ice in the wood else- 
where than in the vessels or wood cells. In the pith the ice, so far as I have 
been able to observe, always occurs within the cells and therefore in very small 
masses." As Wiegand points out, Muller-Thurgau found ice in the large vessels 
and frequently in the wood cells of pear and most distinctly in the grape. 

Frozen twigs of several species were found to expand on thawing, two apple 
twigs, for example, increasing in diameter from 2.97 millimeters and 3.89 milli- 
meters to 3.03 millimeters and 3.95 millimeters respectively. In the willow, the 
only species on which this determination was made, more than half the total 
expansion was in the bark, the percentages being, respectively, 13.5 for the bark 
and 2.5 for the wood. To explain the contraction of twigs on freezing Wiegand 
suggests: "When the water is extracted from the walls of the wood-cells, the 
latter contract to a slight extent just as they do when wood seasons. This ac- 
counts for a part of the shrinkage. The rest and greater part occurs in the cortex. 
Here the intercellular spaces are quite large and numerous and are normally 
filled with air. When freezing occurs the ice forms in the spaces and the cells 
collapse while the air is mostly driven completely out of the twig. The contrac- 
tion in the cortex will be approximately equal to the volume of the air expelled 
plus that of the air compressed minus the expansion of the ice while freezing." 
Curiously enough in all cases studied, except in Populus and Acer and including 
apple, pear and plums, Wiegand found that buds increased decidedly in size upon 
freezing. Prillieux 156 demonstrated conclusively a loss of air and of weight in 
frozen plant tissues. 

Freezing, Not Cold, Kills. — Most investigators do not accept the 
view that, aside from some cases occurring above the freezing point, 
absolute cold kills any plant, whether by "shock," "cold rigor" or other 
effects. Again quoting Wiegand: "Most plants are killed by the first 
ice formation within the tissue. If they survive this, a considerably 
lower temperature is required to kill them, or they may be capable of 
enduring any degree of cold. It has been demonstrated . . . that, in 
the case of delicate tissues at least, death occurs when the ice formation 
has progressed to a certain extent. . . . Death seems due to the actual 
withdrawal of water to form ice, not to the cold. The ice formation 
dries out the cells and the plant suffers therefore from drought con- 
ditions. Every cell has its critical point, the withdrawal of water 
beyond which will cause the death of the cell, whether by ordinary 
evaporation or by other means. It may be supposed that the delicate 
structure of the protoplasm necessary to constitute living matter can no 



WINTER KILLING AND HARDINESS 253 

longer sustain itself when too many molecules of water are removed 
from its support. In the great majority of plants this point lies so high 
in the water content that it is passed very soon after the inception of ice 
formation, hence the death of many plants at this period. Others may 
be able to exist with so little water that a very low -temperature is 
• necessary before a sufficient quantity is abstracted to cause death. 
From some plants enough water cannot be abstracted by cold to kill 
them." Several investigators have shown that certain tissues, cooled 
to a temperature which is fatal if ice formation occurs, will withstand 
that same temperature if ice formation does not occur. 

After investigating several possible ways in which bud scales and wool 
packing might serve to protect the embryo flowers and shoots during the winter, 
Wiegand concluded that their main function is not to shut out cold or even to 
retard temperature changes (about 10 minutes seemed the limit for the greater 
part of any change), but rather to retard the loss of moisture and to prevent me- 
chanical injury especially when the buds are frozen. Lilac buds lost in 3 days, 
at temperatures between — 18°C. and — 7°C, 2.8 per cent, of water when bud 
scales were left on; with bud scales removed the loss of water was 39 per cent. 
Heat absorption due to the color of bud scales in horse-chestnut buds amounted 
to 15°F. Chandler 38 also found that "scales of peach buds do not serve to 
protect them from low temperature. Buds frozen in the laboratory with the 
scales removed were slightly more resistant to low temperature than were buds 
with the scales not removed." 

Freezing and the Deciduous Habit. — The view that death from low tempera- 
tures is due to a withdrawal of water is supported by the consideration that the 
deciduous habit is in most cases essentially a protection against water loss during 
the winter and that the leaves of evergreen plants are particularly adapted to 
reduce the rate of transpiration to a minimum. 

An interesting and suggestive parallelism exists between the autumnal be- 
havior of trees in temperate regio"ns and the changes in trees in regions subjected 
to prolonged dry but warm weather. In both cases they assume a distinctly 
xerophytic character. The most obvious phenomenon accompanying this 
transition is leaf-fall. Of this Coulter, Barnes and Cowles 45 say: "The leaf 
behavior of deciduous trees and of tropical evergreens obviously is related to 
external factors, in the former being associated with climatic periodicity (either 
of moisture, as in the monsoon forests of India, or of temperature, as in the north- 
ern deciduous forests), while in the latter it is associated with uniform moisture 
and temperature. That the deciduous and the evergreen habits are related to 
external conditions may be inferred from many trees and shrubs (e.g., poison 
ivy, Virginia creeper, various oaks) which shed their leaves in regions of cold 
winters, but retain them in warmer climates; furthermore, various plants (as 
the grape and the peach) become evergreen in uniform tropical climates, and 
even those species that remain deciduous (as the persimmon and the mulberry) 
have much longer periods of leafage. 

"The exact factors involved in leaf-fall, that is, in the development of the 
absciss layer, are imperfectly known. In the monsoon forest and in other regions 



254 



FUNDAMENTALS OF FRUIT PRODUCTION 



of periodic drought, it is probable that leaf -fall results directly from the desicca- 
tion incident to the increased transpiration and decreased absorption during the 
dry period. Autumnal leaf-fall in cool climates probably is due to desiccation 
resulting from continued transpiration at a time when absorption is diminished 
by reason of lo\v temperature, although desiccation due to dryness in the soil or 
air may cause the absciss layer to develop in early summer. A severe frost in 
early autumn may retard leaf-fall through injury to the tissues that develop the 
absciss layer. 



"The shedding of leaves at the inception of a cool or dry period is of inestima- 
ble advantage, especially in trees with delicate leaves, because of the enormously 
reduced transpiration thus resulting. The leafless tree is one of the most per- 
fectly protected of plant structures, since impervious bud scales and bark cover 
all exposed portions." 

Accompanying leaf-fall the moisture contents of the various tissues 
change. From summer to early winter there is a considerable lowering 
of the moisture percentage as shown in Table 11, adapted from data by 
Baake et al., 6 showing the moisture percentage in twigs of several varieties 
of apple. 

Table 11. — Percentage Moisture Content of Apple Twigs 



Dormant 


Bud 

swelling 


Blossom- 
ing 


42.43 


48.65 




45.64 


53.31 


65.53 


45.04 


51.66 


62 . 15 


46.32 


52.10 


65 . 57 


46.82 


50.52 


61.87 


47.30 


54.86 


65.79 


43.52 


52.00 


62.62 


47.58 


50.57 


64.48 


48.23 


49.54 


65.22 


47.76 


51.94 
52.56 


63.20 


45.765 


64.19 



Summer 
growth 
period 



Wood 
ripening 



Hibernal 

Oldenburg 

Wealthy 

Yellow Transparent. . . . 

Mcintosh 

Red Astrachan 

Jonathan 

Winesap 

Grimes 

Ben Davis 

Average, 17 varieties 



58.98 
60.50 
61.11 
61.49 
57.76 
60.82 
58.77 
58.67 
58.95 
59.44 

58.92 



53.67 
52.98 
55.04 
51.88 
55.31 
51 . 63 
51.53 
54.16 
51.09 

52.55 



INCREASING HARDINESS 

By Increasing Sap Density. — A logical consequence of the theory of 
death through withdrawal of water by freezing is the correlation of an 
increased sap density (molar concentration) with a lower killing tem- 
perature for any given species. Chandler's investigations have demon- 
strated this. Sap density was increased by various means, such as with- 
holding water, watering with mineral solutions, inducing absorption of 
various substances and it was reduced by shading; in each case with 



WINTER KILLING AND HARDINESS 255 

greater density there was greater hardiness. Unfortunately, attempts 
to increase sap density and therefore hardiness, in peach trees, cabbage 
and tobacco plants, by heavy applications of potash fertilizers were 
not successful in attaining either object. 38 European writers have 
claimed increased hardiness from phosphate or potash applications; 
their evidence, however, is not entirely convincing. 

Wilted tissue, presenting another case of increased sap density through 
withdrawal of water, was tested for hardiness by Chandler with no 
significant results. This seems entirely consistent since the sap density 
in this case is the result, not of the addition of substances in solution, but 
rather of the withdrawal of water and may be closely comparable to the 
initial stage of freezing itself. When a longer and slower wilting appeared 
to be induced on dormant peach twigs, possibly resulting in a somewhat 
more fundamental change in the protoplasm, hardiness seemed increased. 

By Increasing Water-retaining Capacity. — Another consequence of 
the theory that death is due to the withdrawal of water from the cell 
and later from the tissue, is that resistance to cold must be increased by 
factors tending to increase the water-retaining capacity of the cells. 

Observations on the moisture content of apple twigs reported by 
Beach and Allen, 16 shown in Table 13, reveal an important relation to 
hardiness. From July to December there is considerable variation in the 
moisture content of the several varieties. On Jan. 15, however, following 
several days of severe cold, the two hardiest varieties, Hibernal and 
Wealthy, have a noticeably higher moisture content than the tenderer 
varieties; furthermore, the loss of water from July to January is very 
much less in these two hardiest varieties than in the others. 

Data of similar purport, drawn on for Table 12, are reported by 
Strausbaugh 189 in Minnesota. Water losses accompanying markedly 
cold weather were greater in the less hardy plums. Following a period of 
relatively warm weather the less hardy varieties showed a marked 
increase in moisture content, possibly because they were less dormant, 
possibly because they had lost more. 

These observations indicate that the actual moisture content of a 
tissue at most times has less connection with hardiness than its water- 
retaining capacity. The water lost is less significant than the water 
retained. Protection against injury from low temperatures depends on 
the amount of water the plant can retain at a critical moment against the 
great force which tends to draw water out of the cells to form ice crystals 
in the intercellular spaces. This force can be appreciated by the familiar 
ability of growing ice crystals to split rocks. To hold water against this 
influence, the protoplasm must have a certain amount of its moisture 
supply in a form which is not easily frozen. In the section on Water 
Relations plant tissue is shown to contain, in addition to its free and readily 
frozen water, water in an adsorbed or colloidal state, which does not 



256 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 12. — Changes in Water Content of Fruit Buds of Several Varieties 

of Plums 
{Arranged from Strausbaugh im ) 





Stella 
(seminar dy) 


Tonka 
(semihardy) 


Assiniboine 

(hardy) 


Nov. 19 

Dec. 1 

Loss 


50 . 38 

43 . 51 

6.87 


50.51 

43.93 

6.58 


46.51 

45.49 

1.02 


Dec. 26 

Increase 


49.30 

5.79 


50.70 

6.77 


46.80 
0.86 


Jan. 16 


45 . 98 

44.34 

1.64 


44.41 

39.16 

5.25 


47.36 


Jan. 23 

Loss 


47.31 
0.05 


Feb. 21 

Mar. 5 

Loss 


41.98 

39.78 

2.20 


43.24 
40.46 

2.78 


46 . 83 

46.16 

67 


Loss Nov. 19 to Mar. 5 


10.60 


10.05 


0.35 



Table 13. — Moisture Content of Apple Twigs on Different Dates 16 



Variety 


July 15 


Nov. 15 


Dec. 26 

to 28 


Jan. 15 


Decrease 

July 15 to 

Jan. 15 


Delicious 


60.3 


50.5 


50.5 


42.5 


17.8 


Gano 


57.2 


53.2 


51.2 


44.3 


12.9 


Grimes 


60.7 


52.0 


57.7 


43.6 


17.1 


Hibernal 


53.5 


50.4 


52.0 


46.8 


6.7 


Wealthv 


60.4 


50.6 


51.0 


47.5 


9.0 







freeze except at temperatures ranging to — 78°C. If a plant tissue con- 
tains enough adsorbed water, it presumably can withstand any winter 
temperature. Its free water freezes, but there is enough water which is 
not readily frozen to maintain the life of the protoplasm. 

It seems paradoxical that tender plant tissues usually contain more 
water than those which are hardier. In fact Johnston found the ratio 
of water content to dry weight of fruit buds a fairly good index of the 
relative hardiness of certain peach varieties and similar observations have 
been made by many other investigators. However, it is shown presently 
that the development of the water- retaining capacity follows as a reaction 
to a diminished water supply. Hence, there is a direct relation between 



WINTER KILLING AND HARDINESS 257 

the lower total water content of hardy tissues and their greater content of 
adsorbed water which is not readily frozen. Furthermore, the water- 
holding capacity operates less effectively in dilute solutions. 164 

Water in the adsorbed or colloidal condition cannot hold materials in 
solution but may cause higher results in sap density determinations. 
Since in hardy plants there is a smaller amount of free water which can 
hold materials in solution, the sap solutes must be held ordinarily in a 
more concentrated solution than in tender plants. Hence the correlation 
between sap density and hardiness found by Chandler and confirmed by 
other investigators; however, since there is no direct causative relation 
between hardiness and sap density, it sometimes happens that the correla- 
tion does not hold. Pantanelli, 147 for example, was unable to find a 
relation between resistance to cold and molecular concentration (sap 
density) with wheat or beets, though the correlation held for sunflower, 
tomato and corn. 

Clear distinction is necessary between cell water loss and tissue 
water loss. Cell water loss is the cause of death by freezing. Tissue 
water loss must, in many cases, accentuate cell water loss and thus 
indirectly lead to killing. Though the two forms are distinct, in most 
cases each promotes the other. It is probable that some plants are reten- 
tive of cell water and not of tissue water, hence hardy but not drought 
resistant; others are presumably retentive of tissue water but not of cell 
water, hence drought resistant but not hardy. However, there is a 
strong tendency toward parallelism in drought resistance and cold resis- 
tance. The data presented above are based on this parallelism. 

Xerophytic adaptations are well known to students of morphology; 
they serve primarily as protection against tissue loss, but may have an 
ultimate bearing on cell loss and therefore on hardiness. Strausbaugh 189 
shows that the lenticel area on the twigs of a semihardy plum is from 
three to six times that of a hardy variety. He shows also a greater loss 
of water from the twigs of a tender than from those of a hardy variety. 
Thus, occasionally, morphological differences may influence, though 
indirectly, cell water loss. Rather extensive investigations, however, 
have failed to establish consistent morphological differences between 
hardy and tender varieties. Cell water loss, then, must depend on 
something other than structure. 

Water -retaining Capacity Associated with Pentosan Content. — 
Plant tissue which withstands freezing must be supposed to contain or be 
able to manufacture substances which will hold water in an adsorbed or 
colloidal condition. These substances must themselves be colloids, they 
must have a great water-holding and water-absorbing capacity, they must 
be known to occur in practically all plants capable of withstanding winter 
conditions and they must be distributed generally through practically all 
plant tissues. The compounds which answer best to these specifications 

17 



258 



FUNDAMENTALS OF FRUIT PRODUCTION 



are the pentosans, more particularly the water soluble pentosans. Evi- 
dence is presented in the section on Water Relations to show that pentosans 
of some sort are probably the compounds holding water in an adsorbed or 
colloidal condition in plant tissues; this is confirmed by determinations of 
Hooker, 94 given in Table 14, which show a correlation between pentosan 
content and hardiness. 

Table 14. — Pentosan Content of Plant Tissues in Terms of Fresh Weight 94 

(1920 Wood) 



Nov. 8, 1920 



Bases, 
per cent. 



Wealthy 

Yellow Transparent 

Missouri Pippin 

Stayman Winesap 

Ben Davis (short shoots — mature) . . 
Ben Davis (long shoots — immature) 

Currant 

Cuthbert raspberry (mature) 

Cuthbert raspberry (immature) 



6.52 
5.15 



29 
72 
64 
90 



Tips, 
per cent. 



Dec. 2, 1920 



per cent. 



41 
55 

37 

28 
19 
22 



5.99 
5.89 
5.01 
5.26 
5.59 
4.04 



Tips, 
per cent. 



11 
06 
91 
96 
56 
79 



4.78 
5.20 
1.61 



4.44 
3.09 
1.28 



5.01 

4.28 
killed 



3.68 
3.24 
killed 



This evidence supports the idea that pentosans largely determine the 
water-retaining capacity of plant cells, though the particular compounds 
concerned remain to be determined. 

Water Soluble Pentosans in Particular. — Water soluble pentosans, 
such as gums or pectins, seem the most likely to act as water-retaining 
substances. Studies by Rosa indicate that this is the case. Some of his 

Table 15. — Soluble and Insoluble Pentosans in Cabbage and Tomato 

(After Rosa 16i ) 



Total 
pentosan 



Hot-water- 
soluble pectin 



Insoluble 
(by difference) 



Cabbage : 

Tender 

Hardy (dry grown) . . 

Hardy (by exposure) 
Tomato: 

Tender 

Dry grown 

Exposed 



0.215 
0.423 
0.530 

0.693 
0.720 

0.682 



0.075 
0.292 
0.408 

0.070 
0.071 
0.071 



0.140 
0.131 
0.124 

0.623 
0.649 
0.611 



WINTER KILLING AND HARDINESS 



259 



data, reported in Table 15, show the tomato to have a higher total 
pentosan content than the hardier cabbage, but the soluble pentosans 
are quite differently arranged. The increase of total pentosans in 
cabbage of differing degrees of hardiness is due entirely to the increase 
in soluble pentosans; with the tomato, in which no treatment materially 
increases hardiness, there is no increase in soluble pentosans. 

Investigation is likely to show that other substances may exercise 
water-retaining properties and therefore tend toward hardiness. Fat 
emulsions conceivably may act in this way. 

Whatever the compounds may prove to be, their water-adsorbing 
power undoubtedly is affected to a marked degree by the factors which 
generally increase or decrease the water-retaining properties of colloids. 
The effects of nitrogenous compounds and hydrogen-ion concentration 
on hardiness have been emphasized by Harvey and may be of a similar 
nature. 

Pentosan Content, Water -retaining Capacity and Hardiness Respon- 
sive to Environmental Conditions. — The water-retaining capacity of 
plant tissues is increased by any condition which limits the water sup- 
ply without producing actual injury. This is discussed in the section 
on Water Relations. Rosa presents data, given in Table 16, showing 
an increase in the pentosan content of plants hardened by exposure to 
low temperatures in a cold frame. This indicates also that the hardening 
or maturing of plant tissue by exposure to cold is essentially a reaction to 
a limited water supply. 



Table 16. 



-Pentosans of Vegetable Plants in Percentages of Fresh Weight 

(After Rosa 163 ) 





Cabbage 


Leaf lettuce 


Cauliflower 


Moisture series on greenhouse plants 

1. Tender plants grown in wet soil 

2. Medium hardy plants grown with moder- 

ate moisture supply 


0.215 

0.320 
0.423 
0.412 

0.207 
0.413 
0.530 
0.604 


0.106 

0.402 

0.126 
0.230 




3. Hardy plants grown in dry soil 




4. Hardy plants, partly wilted for 2 weeks .... 

Coldframe series 
1. Tender greenhouse plants 


0.191 


2. Hardened 1 week 




3. Hardened 2 weeks 


0.403 


4. Hardened 3 weeks 









Rosa shows also that there is a fairly constant increase in the pentosan 
content of vegetables from early fall until the plants are killed by cold. 
The data in Table 17 indicate that maturity is associated with increased 
pentosan content and greater water-retaining capacity. 



260 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 17. — Pentosan Content of Garden Plants in Percentages of Fresh 

Weight 164 



Date 


Kale 


Cabbage 


Celery 


Oct. 7 


0.511 


0.289 


0.567 


Oct. 20 


0.528 


0.580 


0.801 


Nov. 3 


0.537 


0.545 


0.793 


Nov. 10 


0.722 


0.621 


1.029 


Nov. 18 


1.064 


0.782 





Increased Hardiness with Increased Maturity. — The most generally- 
recognized and most potent single factor influencing killing by cold, 
particularly in tissues withstanding a fair amount of freezing, is the 
degree of maturity attained at the time of exposure. So widely is this 
state recognized in field conditions, that experimental evidence on this 
point, though available, is hardly necessary. Some less known, but 
widely occurring, phases of immaturity in trees are considered later. 
The greater susceptibility of immature tissue to injury from cold is due, 
in part, to the fact that' pentosans or other water-retaining substances 
have not developed : The greater water content of such tissue is evidence 
of the lack of those drying conditions necessary for the proper develop- 
ment of pentosans and hence of maturity. Chandler found no constant 
difference in the moisture content of the twig cortex during the winter, 
though its hardiness varied considerably. With reference to density he 
states: "It would seem certain then that while a part of the increased 
hardiness of tree tissue in winter may possibly be accounted for by the 
greater sap density, not all of it can ; certainly not the greater hardiness of 
December tissue over that of October." The same investigator offers the 
following suggestion based on experimental evidence; "It would seem 
highly probable that, except in the case of cambium, the additional hardi- 
ness acquired by the different tissues of the trees as they pass into winter, 
is a change in the protoplasm such that it can withstand the great loss 
of water rather than a change in the percentage of moisture or in sap 
density." 

RAPID TEMPERATURE CHANGES 

Since maturity is a reaction to dry conditions whether produced by 
exposure to cold or by actual limitation of the water supply, it is logical 
to expect distinct differences in the amount of injury produced by rapid 
freezing when no time is allowed for the development of pentosans and 
by a gradual reduction of temperature permitting an increase in the 
water-retaining capacity of the tissue to develop. 

Killing with Slow and with Rapid Freezing. — The injurious effects 
of rapid freezing seem to have received little attention until the recent 
work of Winkler and of (.'handler. 



WINTER KILLING AND HARDINESS 261 

Winkler, 217 working with dormant twigs that killed at — 22°C. upon rapid 
freezing, found that by small successive reductions of temperature, at — 16°C. 
for 3 days, at -18°C. for 2 days, at -20°C. for 3 days, at -22°C. for 2 days, 
at — 25°C. for 3 days, the twigs were enabled to withstand 12 hours of freezing 
at from -30°C. to -32°C. Chandler 38 reports on the results of his work, 
in part, as follows: "The rate of temperature fall is very important indeed, 
especially in case of winter buds. In fact apple buds can be frozen in a 
chamber surrounded by salt and ice rapidly enough that practically all of them 
will be killed at a temperature of zero F., or slightly below, while it is well known 
that they may go through a temperature of 20°F. to 30°F. below zero with but 
slight injury where the temperature fall is not so rapid . . . the killing tem- 
perature of rapidly frozen twigs was four and a half degrees higher than that 
of the more slowly frozen twigs, and even then the buds of the rapidly frozen 
twigs killed the worst, . . . rapid falling in the early part of the freezing 
temperature clown to — 12°C, does more harm than rapid fall in the latter part 
of the period, from — 12°C. to the killing temperature." "Many young fruits 
and succulent plants were also frozen slowly and rapidly but there was so little 
apparent difference between the results that the data are not given. The killing 
temperature lies so near the freezing point that possibly the slowly frozen tissue 
kills badly because it is exposed to temperatures around the killing point 
longer." " . . . the rate of temperature fall with winter twigs and buds ex- 
erts the greatest influence on the extent of killing at a given temperature of any 
feature we have so far discussed. And in the case of very forward, rather tender, 
fruit buds, the rate of temperature fall exerts great influence. Thus on March 
24, 1913, when all buds, especially the peaches, plums and cherries, had made 
much growth, a temperature of — 11.5°C. killed as many buds with rapid tem- 
perature fall as a temperature of — 16.5°C. with a slower temperature fall." 

A factor involved in very rapid lowering of the temperature is the 
possibility of ice formation within the cells. Though the rate of tem- 
perature fall involved probably does not occur in nature, it may have 
been produced in some of the experiments just described. 

Slow and Rapid Thawing. — Practical men have long held that rapid 
thawing intensifies damage from low temperatures and many investi- 
gators have accepted this view. The fruit grower who heats his orchard 
during the cold nights of the growing season tries just as carefully to 
keep the early morning sun from the blossoms; the young florist is taught 
by older men to supply heat very slowly if accident has lowered the 
temperature of the greenhouse to a critical point. 

Wiegand 214 found that thawing generally occurs at temperatures 
below 0°C, or about at the freezing point ( — 3.5°C. to — 2.3°C. for buds). 
Sudden thawing or several rapid alternations of freezing and thawing 
did not seem injurious. 

It has been held that rapid thawing induces excessive transpiration 
and prevents the return into the cell of the the sap withdrawn in freezing. 
The trend of opinion among recent investigators, however, fails to support 



262 FUNDAMENTALS OF FRUIT PRODUCTION 

this view, it having been found to hold only in a very few cases. As 
already indicated, it can be shown definitely, sometimes at least, that 
death occurs before any thawing begins; furthermore, the method used 
by Sachs and much in vogue among gardeners to induce slow thawing, 
namely, immersion or sprinkling with water, is in reality a method leading 
to more rapid thawing than would occur in air. The water causes a coat- 
ing of ice on the exterior, thus liberating heat to the tissue. Though ob- 
jections might be adduced to this view, the chief matter of interest here 
is that investigators have found, in practically all cases, no difference 
in killing to ensue whether the thawing be rapid or retarded. It should 
be pointed out, however, that there are no reports of inquiry into the 
effect of sunlight on frozen tissue. Injuries due to the effect of light 
on frozen tissue might easily be attributed to rapid thawing. There 
seems to be enough evidence in field conditions of association of sunlight 
and injury to warrant careful study, particularly in view of the increased 
permeability known to accompany increased light. 

VARIATION IN CRITICAL TEMPERATURES 

Definite evidence, under experimental conditions, has shown that 
the critical temperature at which killing results is not a definite point 
for any species, variety or individual plant but is the result of a complex 
of conditions. It probably depends to a great degree on water-retaining 
capacity or the amount of water present that is not readily frozen, but 
other factors may be equally important under certain circumstances 
and unquestionably there are a number of factors affecting the water- 
retaining capacity of the cell colloids. All of these may constantly be 
fluctuating more or less independently of one another and their product, 
the killing temperature, must therefore assume many different values. 
This is abundantly borne out in field observations of winter-killing. 

Summary. — The most tenable of the theories explaining killing from 
cold ascribes death to dehydration of the cells. Ice formation generally 
begins in the intercellular spaces and the process draws water from the 
cells. The water is withdrawn gradually, each decrease in temperature 
being followed by further water loss from the cells, though the rate of 
this loss becomes progressively lower. Death occurs when the dehydra- 
tion proceeds beyond a certain point. The increasing density of the 
cell sap with continued water loss tends to hold the remaining water more 
tenaciously and thus protects the cell somewhat against further loss 
and eventual death. The cell colloids, particularly the water soluble 
pentosans, operate in the same direction and play a still more important 
part. These substances (the water soluble pentosans) develop in some 
plants in response to certain environmental conditions — particularly 
decreasing temperature and a decreased moisture supply. These facts 



WINTER KILLING AND HARDINESS 263 

suggest that certain cultural treatments may be employed to increase 
the hardiness of plant tissue. Rapid freezing is probably more danger- 
ous than slow freezing to plant tissue because there is not time for the 
plant to develop a greater water-retaining capacity; consequently it 
loses a larger percentage of its moisture at a given temperature. Con- 
trary to general belief there is little evidence that rapid thawing is more 
injurious than slow thawing. However, this should not be taken to 
mean necessarily that rapid thawing in bright sunshine is not more 
injurious than slow thawing under cloudy conditions, since the increased 
permeability accompanying increased light may have an influence. 
Critical temperatures for a given species will vary considerably with 
conditions. 



CHAPTER XVI 
WINTER INJURY 

Macoun 120 enumerates ten manifestations of winter injury in orchard 
fruits, viz.: root-killing, bark-splitting, trunk-splitting, sunscald, crotch 
injury, killing back of branches, black heart, trunk injury, killing of 
dormant buds and winter-killing of swollen buds. As one form of bark- 
splitting, Macoun includes a condition considered here as crown rot. 
These forms may occur singly or in varying combinations; some are 
products of severe conditions that almost of necessity entail other forms 
characteristic of less severe freezing; some may be responses of varying 
plant conditions to the same weather and some may be responses of 
identical plant conditions to varying weather. Still other manifestations 
are recorded occasionally. 

Conditions Accompanying Winter Injury. — Nine of the ten forms of 
winter injury distinguished by Macoun 120 appear above ground. This 
diversity is due probably to a wider range of internal conditions in the 
tops and to a wider range in above-ground environmental factors. It 
may be attributed also to the greater facility with which top injuries are 
studied; were observations of parts below ground more easily made, 
what is now referred to simply as root injury might be found to consist of 
several kinds. Above ground so diverse are the manifestations of 
winter injury that the whole condition seems confusion confounded, 
abounding in contradictions. Certain trees in an orchard suffer winter 
injury and others do not. Excess soil moisture causes winter injury in 
one instance and lack of soil moisture causes it in another. Cold leads 
directly to winter injury yet sometimes high temperatures induce it 
hardly less directly. At times young trees suffer more; at others, older 
trees. Orchards in high wind-swept spots are damaged; again it is the 
low-lying orchards that are afflicted. Late maturing trees suffer in one 
locality; somewhere else it is the early maturing trees. Now it is trees 
weakened by neglect that lack hardiness; again it is the highest cultivated 
trees that fail. An early winter freeze is the cause at one time; in another 
case a late winter freeze brings destruction. An early freeze has been 
known to kill peaches while pecans survived. 

Table 18, arranged from data assembled at the New York Agri- 
cultural Experiment Station, at Geneva 140 and showing climatic condi- 
tions at that point, is designed to show the varying conditions that may 
induce or accompany winter injury. Unusual climatic features that 
have, conceivably, a bearing here, are shown in heavy type. The 

204 



WINTER INJURY 



265 



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266 FUNDAMENTALS OF FRUIT PRODUCTION 

highest and the lowest rainfalls for August, September and October, the 
highest mean temperatures for August, September and October and 
the lowest mean temperatures from October to February are thus distin- 
guished and the minimum temperatures for each month indicated. 
The winters of 1895-1896, 1903-1904 and 1917-1918 may be considered 
the seasons of greatest winter injury for this section in recent years. 
It is evident at once that the rainfall preceding the winter of 1895-1896 
was the lowest of any season reported; that preceding the 1903-1904 
season was the highest and that preceding the 1917-1918 winter was very 
close to an average. The three destructive winters were, then, preceded 
by both extremes and an average rainfall. Though the rainfall for the 
months considered was in 1897 only 0.02 inch more than that of 1896, no 
serious damage was reported; though the rainfall for these months in 
1915 was only 0.58 inch less than that of the same period in 1903-1904, 
no widespread damage followed. 

The seasons with highest average temperatures for the last of the grow- 
ing season, 1900 and 1906, were not followed by the greatest destruction. 
The lowest monthly temperatures for October, November, January and 
February came in years not distinguished for greatest winter-killing. 
Only in December did the lowest monthly temperature occur in a winter 
of extensive injury. The absolute minima for October, for November 
and for January fall outside the years of greatest damage. 

Reviewing by seasons: the 1895-1896 winter shows extreme condi- 
tions (heavy type) in low rainfall and low late winter temperatures; the 
most noteworthy divergence of the 1903-1904 winter was the heavy 
rainfall, while for 1917-1918 the high and low monthly precipitations 
combined to make an average rainfall and the noteworthy features for 
that winter were the low temperatures of November and December. Not 
far from Geneva, at Ithaca, Bailey 8 wrote of the 1895-1896 winter, "the 
phenomenal injury wrought by last winter was probably not wholly the 
result of low temperature. The drought of the last summer and fall no 
doubt augmented the injury." In reviewing the winter of 1903-1904, 
for states east of the Mississippi, Stockman 188 stated that the severity 
"was not due to occurrence of very low minimum temperatures but to 
the number and succession of days whose mean temperatures continued 
below the normal ... At only two stations having 25 years or more of 
records was the record of lowest temperatures broken. No record of 
minimum temperatures at a regular Weather Bureau station was broken 
during December and February." 

It seems, then, that an extreme of any one feature of the climate is 
not of itself likely to cause widespread injury, but that injury depends 
considerably on a combination of accentuated, rather than on isolated 
extreme, conditions. Thus 1895-1896 may be described as in many ways 
a characteristic Dakota winter in its drying out effects; in 1903-1904 



WINTER INJURY 267 

late maturity with late cold and in 1917-1918 immaturity and early 
cold are the distinguishing features. 

Speculation is uncertain but in this case rather interesting. It can- 
not, of course, be proved but it seems possible that had the rainfalls of 
1895 and 1917 been exchanged the damage would have been less in both 
cases; or, had the rainfall of 1915 been combined with the August-October 
temperature of 1900 and the November minimum of 1904, how great 
might have been the danger! Out of the 35 seasons covered in Table 
18, only six have no notable climatic extreme to be recorded. 

Winter Injuries Classified.— Winter-killing of hardy fruits in temper- 
ate regions, then, may depend on: (1) a lack of maturity in tissues, (2) 
a lack of ability to resist winter drought conditions, (3) too ready response 
to short periods of warm weather in the winter. These are listed 
here in the probable order of their relative importance and frequency, 
though in any given section the sequence may be changed. In the 
Minnesota-Dakota section, for example, it is probable that winter drought 
and absolute cold are more frequently the causes of winter-killing; in the 
northeast the lack of maturity of tissues is probably the one dominant 
factor, while farther south much of the winter-killing of buds is the result 
of the breaking of dormancy by unseasonable warm weather, followed by 
ordinary cold. 

These classes can be recognized in many cases by the form of the resul- 
tant injury, though sometimes different causes appear to have nearly 
identical effects. Crown injury and crotch injury may be related 
with some certainty to lack of maturity. Killing back of branches results 
from the same factor, but may be regarded also as a sign of varietal ten- 
derness or it may be caused by winter drought. Killing of apple fruit 
buds in northern sections appears to be a result of absolute cold, but with 
peaches in climates such as that of Missouri it is to a considerable extent 
induced by ready development before cold weather has passed. Winter 
sun-scald is a localized manifestation, ordinarily, of a late winter freezing. 
Trunk splitting is frequently associated with an immature condition and 
at times with a sudden and considerable drop in temperature. 

The diversity of causes and multiplicity of effects make it quite evi- 
dent that any attempt at setting definite temperatures as injurious or fatal 
without regard to other conditions is futile. Though there is a generally 
accepted belief that — 14°F. is fatal to peach fruit buds, they have been 
known to survive — 20°F. It is not always the coldest winter that does 
the greatest damage. Much depends on the character of the preceding 
autumn, whether it induced proper "ripening" of the wood or forced 
late growth and on the period at which the cold weather occurred; of 
course much depends on the treatment accorded any given orchard or 
tree during the preceding summer and autumn. 



268 FUNDAMENTALS OF FRUIT PRODUCTION 

INJURIES ASSOCIATED WITH IMMATURITY 

Early maturity of wood is of paramount importance in most of the 
northeastern United States and is by no means a negligible factor outside 
that region. Most of the injury in Washington state orchards in the 
disastrous freeze of late November, 1896, can be attributed clearly to 
immaturity rather than to the actual temperature ( — 12°F.) attained. 12 
Any region with a comparatively short growing season and with fairly 
heavy late summer and autumnal rainfall is subject to winter killing 
because of immaturity. Other combinations of conditions may produce 
occasionally the same susceptibility in regions ordinarily free from these 
dangers. Thus in most irrigated sections climatic conditions are such 
that injuries of this type are not to be expected; however, they are fre- 
quently brought about by the injudicious use of irrigation water early 
enough in the autumn to prolong growth. In the freeze of 1896, in 
Washington, most of the orchards that had been irrigated in late summer 
suffered more than others. 12 Late irrigation should be very late, if 
immunity to this form of injury is to be insured. Furthermore, it should 
be borne in mind that maturity is only a relative term, the so-called 
"maturity" of the Willamette valley, for example, being quite different 
from the "maturity" of Wisconsin. Therefore, a given temperature, 
common in Wisconsin but unusual in the Willamette, might be harmless 
in the one location but very injurious in the other, even to trees of the 
same variety. 

Much of the damage from winter temperatures in England and in 
northern France and Germany is evidently associated with lack of ma- 
turity, since particularly cool summers followed by winters of moderate 
severity have frequently proved more damaging than colder winters that 
followed favorable growing seasons. A "cold winter" for England 
would be considered mild in the northern states or Canada; in England 
it might cause considerable damage and none in New York or Michigan. 
The prevalence of "frost cankers" as the chief manifestation of winter 
injury in England lends weight to this view. 

Affecting More or Less the Entire Plant. — Emerson 60 states: "Resist- 
ance to cold in trees is due often almost wholly to the habit of early 
maturity rather than to constitutional hardiness. Black walnut trees 
at the Experiment Station (Nebraska), grown from northern seed, by 
virtue of perfect maturity, passed through the extremely severe winter of 
1898-1899 without apparent injury while similiar black walnut trees from 
southern seed, owing to imperfect maturity, have had their new growth 
killed back from a few inches to two or three feet for the past six years and 
yet notwithstanding this great difference in resistance to cold in winter, a 
comparatively light freeze late in the spring of 1903 killed the new growth 
of the northern trees just as completely as it did that of the southern ones. 



WINTER INJURY 269 

Northern trees are constitutionally no hardier than southern but their 
superior resistance to winter cold was due to their habit of ripening their 
new growth perfectly in the fall." 

Macoun 118 introduces evidence to the same effect: "From the writer's 
experience with over 3,000 species and varieties of trees and shrubs, 
exclusive of cultivated fruits, from many countries and climates, which 
are under his care and observation at the Central Experiment Farm, 
Ottawa, we have drawn the following conclusions regarding the hardiness 
of trees; A tree or shrub which will withstand a test winter at Ottawa 
must be one which ripens its wood early. Trees or shrubs which are 
native to places having a longer or much longer growing season than at 
Ottawa grow larger than native species or those from a somewhat similiar 
climate to the native species, and when a test winter comes their wood is 
not sufficiently ripened, or winter-resistant, and they are more or less 
injured or perish. . . . Another observation regarding tender trees has 
been that after a season when the growth has been strong more injury is 
likely to occur than in a season when the growth is short . . . the 
season of all the hardiest varieties [of apples] is summer or autumn . . . 
apples which mature early and are in condition for eating in summer and 
autumn are grown on trees which ripen their wood early, and, on the other 
hand, an apple which is not ready for use until winter is usually grown 
on a tree which does not ripen its wood early." 

Attention may be called to the doubtful wisdom of fall planting in 
northern regions of trees grown far to the south. These trees, to be 
shipped in time for planting in the north, must be dug when they are 
still quite immature. They are, if planted in the fall, exposed to cold 
winter temperatures and are thus doubly at a disadvantage. It is true, 
the digging may in itself induce a degree of maturity through drying out, 
but hardly as much as would be attained by trees grown farther north. 
The wisdom of delaying digging as long as possible is obvious. 

Tender Plants may be More Resistant than Hardier Plants. — A tempera- 
ture of 15°F. at South Haven, Mich., on Oct. 10, 1906, uniformly 
killed peach trees while pecans, in the same orchards, survived. 194 Here 
is undeniable evidence of a tender species being more hardy at that time 
because of maturity than a species that is far more hardy in its mature 
condition. Similarly, records show that apple trees planted 2 and 
3 years in Wyoming were killed by a temperature of 12°F. in Septem- 
ber, when they were still in full leaf, 29 though there are numerous instances 
of trees surviving approximately equal temperatures without material 
injury when they were partly leaved out in the spring. 

The Effect of Summer Conditions Favorable for Late Growth. — During 
the winter of 1903-1904 in Ohio, though the chief damage was to trees of 
low vitality, vigorous trees succumbed in numerous cases. These were 
almost invariably in "low, moist, rich black soil favoring extreme growth 



270 



FUNDAMENTALS OF FRUIT PRODUCTION 



of soft, poorly matured wood, or in orchards in rich soils, receiving late 
cultivation." 81 Emerson 58 found similar susceptibility in peaches grow- 
ing in rather moist soils or receiving late cultivation in Nebraska. Zero 
weather or even 6°F. above is considered more harmful in very early 
winter in Montana than -30°F. or -40°F. later. 63 

Selby 177 supplies other interesting cases of injury in Ohio associated 
with immaturity. In 1880-1881, late cultivation in two orchards, 
accompanied by heavy August rainfall and normal September rainfall, 
produced heavy and prolonged growth. Late November brought zero 
weather; the December minimum was -13°F. These temperatures 
ordinarily are of no great significance but in this case they caused complete 
destruction of Baldwin apple trees. On a larger scale and over a wider 
area, the same climatic conditions, when approximated in the growing sea- 
son of 1906, were followed by widespread winter injury. In this case the 
following winter was severe but, as is shown in Table 19, arranged from 
Selby's data, in no month of this winter did the temperature closely 
approach recorded minima. It was definitely established that much of 
the injury was done by a temperature of + 18°F. on Oct. 12. The 
unusual features of these two damaging years were, not the winter 
temperatures, but the summer and fall temperatures and rainfall. 



Table 19. — Climatic Conditions Accompanying Winter Injury in Ohio 177 



Month 



Temperature (degrees Fahrenheit) 



1880 



Mean 



Mini- 
mum 



Average 23 
years 



Mean 



Mini- 
mum 



1906 



Mean 



Mini- 
mum 



Rainfall (inches) 



1880 



Average 
23 years 



1906 



May 

June 

July 

August. . . 
September 
October . . . 
November 
December. 

January. . . 
February . 
March. . . 



65.8 
63.4 
74.5 
71.0 
64.8 
52.3 
33.9 
25.7 



35.5 

45.5 
52.0 
48.0 
41.5 
30.5 
-5.0 
-13.0 



61.2 
69.7 
73.9 
71.5 
65.5 
53.5 
40.9 
31.1 



:r2 



61.3 
69.8 
72.1 
74.6 
68.9 
52.7 
41. 1 
32.3 



1.24 
5.65 
6.06 
5.03 
2.02 
2.27 
2.39 
1.06 



3.63 
3.94 
3.37 
3.04 
2.71 
2.13 
3.05 
2.74 



2.17 
3.41 
5.14 
4.77 
2.92 
3. 19 
2.59 
3.68 



1881 



1881 



1907 



24.2 
29.0 
35.6 



-2.0 

-2.5 

13.0 



32.2 
26.0 
45.9 



-23 
-19 
-2 



1.31 
3.25 
2.75 



2.70 
2.66 
3.39 



6.11 
0.85 
5.55 



"Second Growth" Particularly Susceptible. — Excessively dry summer 
weather also, if followed by a fair precipitation in early autumn, may 
result in immature wood at the entrance into winter. 211 The dry sum- 
mer may cause a "premature dormancy" followed by second growth. 



WINTER INJURY 271 

Instances of this are furnished sometimes by the fall blossoming of fruit 
trees. The severe winter of 1917-1918 resulted in greater damage to old 
trees in Indiana than to young and the suggestion is made that this con- 
dition "is possibly accounted for by the fact that many old trees made a 
late second growth while on vigorous young trees the growth was not 
arrested by dry weather in late summer and they matured normally." 79 
It is interesting to contrast this condition with the greater damage to 
young trees in Ohio following the wet summer of 1906. 

Preventive Measures. — Unfortunately the weather cannot be predicted 
reliably far ahead. However, it seems evident that August rainfall 
frequently is important in the northeast in determining tree maturity 
in October and that orchard operations in that section should be varied 
somewhat during August according to the rainfall. A very dry August 
should be accompanied by late cultivation to lessen the likelihood of 
second growth; a very wet August would indicate the wisdom of stopping 
cultivation altogether and sowing a quick-growing, moisture-consuming 
cover crop. A warm, moist October cannot be foretold but its effects 
can be forestalled, at least in part, by a suitable cover crop which will 
reduce soil moisture. 

Localized Injuries. — Aside from the occasional serious and widespread 
damages just mentioned, there are, probably every winter, minor localized 
injuries. It is impossible, however, to draw any sharp line between 
what is here termed localized injuries and more general injury. For 
instance, the killing back of shoots, canes or limbs, if severe, would be 
considered in the latter class; if it were light it might as readily be con- 
sidered localized. 

Crotch and Crown Injury. — A form of injury, often unnoticed for 
some time after its occurrence, but with greater potentiality of ulti- 
mate serious consequences, is the killing of more or less limited areas 
of bark on the trunk, particularly at the crown of the tree or at the 
crotches. Attention may be drawn to the dead area first by its sunken 
appearance consequent to the growth of the surrounding uninjured tissue 
or it may become evident through the cracking of the bark at the injured 
area or. sometimes by the loosening of the bark. 

Of the apple varieties commonly grown in the regions where this 
injury has been most studied, Ben Davis seems most susceptible, with 
Baldwin showing considerable tenderness in this respect. King, though 
less widely grown, is so notoriously subject to this malady that the injury 
is sometimes called the "King disease." It seems significant that all 
of these varieties are late growers. Gravenstein, in Nova Scotia, is 
also reported as susceptible. 118 

Grossenbacher 82 reports crown rot much more common in cultivated 
land than in sod and particularly in land formerly in sod but recently 
plowed. He also reports high, wind-swept situations with thin soils to 



272 FUNDAMENTALS OF FRUIT PRODUCTION 

be more subject, though it seemingly appears in any situation. No 
one side of the trees is uniformly injured, according to his observations, 
though all cases occurring at any one time in a given orchard are likely 
to be confined to some particular exposure. Trees which have made a 
rather unusually large, or rather late, growth appear more liable to 
injury. 

In the 1913 freeze, in the citrus regions of California, the crotches 
were the parts of the trunk found most damaged. 206 Crotch injury 
and those forms of crown rot not due primarily to the attacks of parasitic 
organisms are probably most frequently associated with early winter 
injuries associated with immaturity. Consequent to the winter injury, 
fungus infestation of the dead area may appear but, excepting the fire- 
blight bacillus, no organism has been shown definitely to be the primary 
causative agent in producing this disorder. 

Localized Injuries and Delayed Maturity. — Chandler 38 states: "The 
wood at the base of the trunk and at the crotches of all rapidly growing 
branches seems to reach a condition of maturity in early winter more 
slowly than does other tissue." 

This view corroborates studies by Mer 131 on the duration of cambial 
activity in various trees, reported in part as follows. "Just as it awakes 
gradually in the different regions of a tree cambial activity ceases pro- 
gressively at the end of summer. ... It disappears from the branches 
before disappearing from the trunk. In trees that are closely grouped, it 
leaves first the low branches, less vigorous than those of the top, and the 
basal and median parts of these branches before their extremity. It is 
only following this that it leaves the higher shoots. In the large branches 
of an isolated tree it stops earlier at the tips than at the middle. It is at 
the level of the basal swelling that it persists the longest. In the trunk 
it stops first at the top, then at the middle and finally at the base. When 
growth is not very active it ceases, on the contrary, earlier in the lower 
region. ... It is in the portion of the trunk situated immediately 
below the soil that cambial activity is confined last. 

"It is evident that in the regions of the trunk where the vegetative 
activity is the most pronounced, because they are the youngest or 
because they are the best nourished, that cambial activity awakes 
first. . . . It is there also, that in general, it stops latest. On the other 
hand, in all circumstances where growth is slow, we see cambial activity 
manifesting itself slowly and stopping earlier. . . . Between the length 
of the cambial activity and its intensity there is, then, a manifest 
relation." 

This statement seems in itself adequate explanation for much of the 
localization of winter injury associated with immaturity. Field studies 
in several regions seem to correlate immaturity with this type of injury 
rather uniformly. 



WINTER INJURY 



273 



Contributing Factors. — The drying effect of wind should be considered, 
as also the effect of cold winds on the temperature of the exposed tissues. 
Winter killing is sometimes more severe in the three or four rows nearest 
the windward side of the orchard. Many of the older prune orchards in 
the northern end of the Willamette valley still showed, 15 years later, 
the marks of the freeze of November, 1896, in the shape of dead areas on 
the northwest sides of the trunks, corresponding to the direction of the air 
drift at the time of the freeze. In many cases of this sort the dead tissue 
ceases abruptly at the point where snow stood at the time of the injury, 
suggesting at least that the injury was due to the temperature effect of 
the wind. The effect of snow on soil temperatures will be shown 
later. This protective influence evidently is not confined to the soil, 
as data shown in Table 20 clearly indicate. 

Table 20. — Temperature Under 10-Centimeter Snow Covering 

(After Goeppert 1 **) 



Date 


Under snow, 
degrees Centigrade 


Air, 
degrees Centigrade 


Feb. 4 

Feb. 5 


-3.0 
-4.6 
-6.5 
-6.0 
-5.0 
-2.0 
-1.5 


-12.6 
-14.7 


Feb. 8 


-16.7 


Feb. 10 

Feb. 11 

Feb. 13 

Feb. 15 




-14.9 
-15.8 

- 5.7 

- 2.8 



Consideration should be given, also, to the unequal maturing of 
tissues on different sides of the tree trunk. Casual observations in 
autumn have indicated that maturity may be attained more rapidly on 
one side of the stem than on another. It would follow, then, that a given 
temperature in autumn might prove injurious to the tissues of one side 
and not of the other, without the intervention of other causal agents. 
Furthermore, it should be considered that the temperature a few inches 
above the soil may be, on clear cold fall nights, 10° colder than is indicated 
by a shelter thermometer, so that an official temperature record of 20°F. 
may mean that the tissues at the crown were exposed to a temperature 
of 10°F. 

Remedial Measures. — In view of the different circumstances under 
which this type of injury occurs it is probable that not all the factors 
mentioned are operative in any given instance and that only one of them, 
if sufficiently intensified, may produce the injury. The one condition 
apparently requisite to crown rot and to crotch injury is immaturity 
in the tissues at the point involved. The prospective grower is safe in 

18 



274 FUNDAMENTALS OF FRUIT PRODUCTION 

utilizing protection, natural or created, from winds, particularly those 
prevailing in early winter, and the grower whose orchard is on an exposed 
site should pay careful attention to the attainment of as complete 
maturity as possible in his trees. Banking, though laborious and 
expensive, is justified under threatening conditions. For trees already 
damaged the best treatment is to cut away the injured bark and to cover 
the exposed surfaces with grafting wax or paint and possibly to 
bridge-graft. 

WINTER INJURY ASSOCIATED WITH DROUGHT 

In spite of the great water-retaining capacity of the tissues of the 
most hardy deciduous fruits in a dormant state, they are not able to 
withstand an indefinite amount of desiccation. Especially when the 
evaporating power of the air is high they gradually lose water. This will 
result eventually in a desiccation that may mean the death of the tissue 
unless the water lost is replaced promptly. Recovery from winter 
desiccation, or the ability to withstand long continued hard freezing 
(physiological drought) or long continued winter drought (atmospheric), 
depends therefore on a supply of available moisture upon which the 
roots may draw. In many sections there is seldom, if ever, a winter 
when soil moisture would be a limiting factor in this connection. In 
others it is frequently a limiting factor and gives rise to those injuries that 
are classed here as associated with winter drought. 

Fundamentally all injury to dormant tissues from cold is to be regarded as 
induced by drying out. Paradoxically, it is generally the tissue containing the 
most moisture that is most subject to damage. The injury, however, comes from 
immaturity and not from excess moisture. Apparently there is a certain quan- 
tum of water, varying with the kind of plant and with conditions, that is essential 
to protoplasmic life and this is retained more tenaciously by mature tissue. 
Hence, in considering winter injury a distinction must be drawn between mois- 
ture in the plant tissues (water of composition and surplus moisture) and 
moisture in the environment. Though the two are closely related, freezing 
(drying out) of immature tissue in a moist environment should be distinguished 
from freezing (drying out) due to dry environment though the final lethal 
process is the same. 

Immaturity and Winter Drought 

Injury from drying out may have certain manifestations in agreement 
with that from immaturity. It is, however, somewhat more evident 
in the tops though it may extend to the trunk. Fruit buds in the apple 
are killed more generally by this type of freezing than through imma- 
turity. Wood formed the previous year suffers heavily; with more 
extreme conditions the damage extends downward. Injury associated 
with immaturity may start either on the young twigs or on the trunk. 



WINTER INJURY 



275 



In one case the young twigs suffer because they are immature; in the 
other because they are the most subject to drying out, just as they would 
be in excessive growing season drought. Winter drought injury may 
discolor wood on older parts of the tree but it does not kill cambium 
readily. 

It should be remarked, also, that in some regions it is quite conceiv- 
able that much of the winter killing in the tops may originate primarily 
as root killing. Conditions there are favorable to root injury and it has 
been definitely shown many times to occur. Early winter root killing 
would be followed by a drying out of the top. The latter symptom natu- 
rally would be more evident and would pass as killing of the top, the 
true cause being obscured. However, the preventives for both classes of 
injury agree in requiring a high soil moisture content after danger of 
inducing late growth has passed. 

Water Loss from Dormant Tissues 

Some measure of the loss of water by dormant trees is afforded by the 
data presented in Table 21 showing decreases in weight of 8-year old 
apple trees during two winters in Wisconsin. 165 Obviously these losses 
are in trees severed from their roots. If the loss in moisture of standing 
trees, where the supply of water would be renewed to some extent, should 
be determined, it would be considerably greater but the degree of exhaus- 
tion would be less because, as has been shown earlier, the loss by evapora- 
tion diminishes as the degree of exhaustion increases. If the dry weight 
of the trees could be deducted, the percentage loss of moisture would be 
correspondingly increased. Quite noticeable are the differences in 
moisture losses during the two winters recorded in Table 21. The winter 
of 1903-1904, though severe, was moist and many cloudy days occurred. 
There was little winter injury in Wisconsin during that season. 



Table 21. — Loss in Weight of Apple Trees During Two Winters 165 

(Weight, pounds) 



Date 


Tree 1 


Tree 2 


Tree 3 


Tree 4 


Dec. 19, 1902 


36.6 


24.6 


35.7 


30.4 


Feb. 27, 1903 


34.7 


23.5 


34.4 


29.0 


Apr. 3, 1903 


31.4 


21.4 


31.6 


26.5 


Loss 


5.2 
26.2 


5.2 
24.2 


4.1 


3.9 


Dec. 5, 1903 




Mar. 26, 1904 


25.6 


23.6 








0.6 


0.6 







276 FUNDAMENTALS OF FRUIT PRODUCTION 

Bailey 204 estimates that a large apple tree loses from 250 to 350 grams 
of water each day through the winter. Observations on moisture content 
of apple twigs in Iowa show an actual increase from November to Decem- 
ber in many varieties; on Jan. 15, however, following several days of 
severe cold, there was a very marked decrease, though the respective 
intervals between observations were 5 weeks and 3 weeks 16 (see Table 13). 

Water Conduction in Trees During the Winter 

Bailey 10 cites evidence gathered in New York showing loss of moisture 
in twigs during winter and a higher moisture content during a thaw than 
during a previous period of cold weather, indicating a conduction of sap 
during the milder weather. Indeed such a conduction must be conceded 
else the tree would inevitably dry out. Wiegand 213 showed a conduction 
of water to Pinus Laricio buds at temperatures between — 18°C. and 
— 6.7°C. Buds severed from the tree but sealed immediately on the 
cut surfaces showed an average water content of 41.2 per cent, after 3 
days while buds taken fresh from the tree at the end of this time, even 
though the twigs had been frozen, showed an average content of 47.5 
per cent. It is probable that interference with conduction, or an evapora- 
tion rate much higher than conduction, is just the condition requisite for 
winter drought injury. 

Relation of Freezing to Water Conduction. — It is well known to every 
wood-chopper of the northern woods that trees freeze even to the center 
in prolonged cold weather. Investigations have shown that in trees of 6 
to 8 inches diameter the difference in temperature between the center and 
the outside in the morning is only 1° or 2°R., though in trees 2 feet in diam- 
eter it may be on single days 5°, 6° or 7°R. ; with air temperatures of — 13° 
to — 15°R. the tree temperature was —12° to — 14°R.; most important, 
the longer the temperature of the air remains uniform the more the tem- 
perature of the tree approaches that of the air. m The temperature of the 
alburnum or sap wood in maple has been shown to follow the air tempera- 
tures fairly closely. 100 More detailed figures taken morning, noon and 
night, at a depth of 8 centimeters in a box elder tree, indicate that tree 
temperatures follow the trend of the air temperatures very closely, not, 
however, reaching the full extremes of the outside fluctuations unless 
these are maintained for some time. 185 Figure 27, arranged from a part 
of these figures, shows typical daily fluctuations of air and tree tempera- 
tures. Table 22 shows the averages of the temperatures recorded during 
January and February. Observations in Lapland show winter tempera- 
tures in live and dead trees to be practically the same. 65 

Grape vines have been grown in a greenhouse, so trained that certain 
canes passed outside and were then brought back into the house. The 
base and the upper parts, inside the greenhouse, opened their buds 
quickly and continued to grow. On cold mornings, however, with the 



WINTER INJURY 



277 



outside temperature around — 10°C, the leaves on the upper part of 
the stem were very much wilted, because of the interference with sap 
conduction in the portion of the stem outside. With rising temperature, 
however, they recovered. 57 




10 



12 



13 14 15 
February 

Fig. 27. — Temperature fluctuations in a tree trunk. 



(After Squires 185 ) 



Table 22. — Tree and Air Temperatures 
(After Squires 185 ) 





January 


February 




Air, degrees 
Centigrade 


Tree, degrees 
Centigrade 


Air, degrees 
Centigrade 


Tree, degrees 
Centigrade 


6 to 7 a.m 

12 to 1 p.m 

6 to 7 p.m 

Entire dav 


-10.84 

- 6.60 

- 9.20 

- S.88 


-9.37 
-8.90 
-7.50 

-8.57 


-11.93 

- 4.35 

- S.65 

- 8.31 


-10.46 

- 7.55 

- 7.00 

- S.34 



These considerations make it evident that prolonged cold weather 
must interfere materially with sap conduction while at the same time the 
conditions accompanying extreme cold are the very conditions which 
favor greater drying out. It should be considered, too, that the conduc- 
tive regions in the tree are near the outside of the stem. Many cases of 
twig killing must, therefore, be considered as due to drought, short, 
perhaps, but intense in localized areas. Possibly the greater suscepti- 
bility of twigs to this injury is not due entirely to failure in conduction 



278 FUNDAMENTALS OF FRUIT PRODUCTION 

but may be explained in part by the lack of a sufficient amount of sap- 
wood to serve as a local reservoir. Even prolonged cold does not affect 
the upper part of tall trunks as much as it does the low, smaller branches 
though conduction from the ground is conceivably as difficult; the tissues 
on the trunk, however, have both relatively and absolutely a greater 
amount of sapwood on which presumably they may draw. 

Where Winter Drought Conditions Prevail 

Winter drought conditions are in a measure independent of soil con- 
ditions and can be considered as of possible occurrence over a wide range 
of territory. The coldest weather in humid sections is accompanied by 
dry atmospheric conditions; occasionally after a dry summer and fall 
these sections suffer from winter killing due to desiccation. Long con- 
tinued severe, though not excessive, cold would induce physiological 
drought. The winter of 1895, already mentioned, was of this type. It 
is, however, infinitely more common, in proportion to the amount of 
fruit grown, in regions of prevailingly dry atmosphere and intense cold. 
Wyoming, the Dakotas and parts of Minnesota furnish abundant 
examples. Rainfall is comparatively light in those sections and the soil 
frequently freezes with a low moisture content. Winter precipitation is 
less than summer, frequently only a fourth as great and there is much 
clear, cold weather. 

Protection Against Winter Drought Injuries 

Necessarily protective measures against winter injury associated with 
drought must be preventive. They must either reduce water loss or 
increase water supply. 

Winter Irrigation. — Buffum 29 advocates in Wyoming thorough irriga- 
tion "late in the fall, before the ground has frozen and when growth 
has ceased. The later this irrigation can be done the better as the 
object is to store moisture in the soil sufficient for winter . . .where 
orchards are planted on bottom lands that have a continual supply of 
moisture fall irrigation may be unnecessary. But on upland it is the 
surest way to prevent trees from winter killing and when possible irri- 
gations through the winter will be found advantageous." In North 
Dakota, Waldron 199 writes: "Parts of our own plantation have been 
cultivated every year until the ground freezes with only the best results 
. . . the treatment that provides the trees with the greatest amount 
of soil moisture in the fall will tend to prevent winter killing." Else- 
where the same writer states: "The cause of winter killing in mild 
weather is the drying up of the twigs .... Trees and shrubs that are 
neglected during the latter part of summer so that the ground becomes 
hard and dry, ripen their wood prematurely and unless fall rains are 
abundant the drying process sets in before winter begins, leaving the 



WINTER INJURY 



279 



plant in poor shape to endure further drying. . . . Some of the plants 
that defer this change (to winter condition) the longest are among the 
hardiest we have." 200 

Cultivation. — Experimental demonstrations with Wealthy apple trees, 
on 15 widely separated farms in South Dakota, give quantitative 

Table 23. — Effect of Cultural Conditions on Winter Killing in South 

Dakota 128 



Lot 
number 


Number 
trees, 
1916 


Number 

trees dead, 

1919 


Number 

trees 

severely 

injured, 

1919 


Number 

healthy 

trees, 1919 


Average 
growth 
(inches) 


Average per- 
centage of 
soil moisture, 
Nov. 15 


Average per- 
centage of 
soil moisture, 
Feb. 15 


1 

2 
3 

4 


50 
50 

50 
50 


41 
16 

22 
7 


7 
18 
13 
11 


2 
16 
13 
32 


2.0 

9.0 

6.5 

15.0 


14.70 
17.95 
15 . 50 
31.50 


14.2 

19.2 
15.2 
33.8 



verification of the opinions just quoted (Table 23). Lot 1, showing the 
lowest moisture content and the greatest injury to trees, was composed of 
trees planted in prairie sod; Lot 2 was cultivated each 10 days till Aug. 
10; Lot 3 was "cultivated each 10 days till July 1, followed by a cover 
crop of fall rye or buckwheat" and Lot 4, which showed least injury, 
was cultivated each 10 days until Aug. 10, just as Lot 2, but in addition 
received a heavy watering just before the ground froze for the winter. 
The investigator concluded that "summer cultivation is positively needed 
and in very dry seasons fall watering or irrigation of some sort is not 
only advantageous but necessary." 

Cover Crops. — Another point of interest here is the lower soil moisture 
in the cover crop lot and the somewhat greater attendant injury, as 
compared with the clean cultivated lot. Had a winter favorable to 
root killing intervened, the results in these two plots might have been 
different. However, the danger from cover crops in this region of light 
rainfall is apparently more frequently present than the danger from their 
absence which is discussed presently. This point doubtless has occasion- 
ally equal application in dry situations in other regions. Comparison of 
these results with those of Emerson, reported below, indicate that the 
best insurance against winter injury in general in this region — and in 
occasional sites in more humid sections — is a frost-tender cover crop 
with a heavy late fall irrigation. To be sure, in those districts where 
irrigation water is not available, the preventive measures against the 
winter injuries associated with drought must of necessity be incomplete. 
However, the recognition of the liability of a given site to this form of 
injury may enable the grower so to shape his cultural practices early in 
the season as to minimize the danger. 






280 



FUNDAMENTALS OF FRUIT PRODUCTION 



Studies by Emerson 59 in Nebraska show the effect of cover crops of 
different kinds on the hardiness of young peach trees. The cover crops 
are considered in two classes, frost-resistant and frost-killed. Table 24, 
reproduced from Emerson's report, shows the effect of these crops on soil 
moisture content. 

Table 24. — Effect of Various Cover Crops on Soil Moisture During the Fall 

of 1900 59 



Kind of cover crop 


Sept. 20 


Oct. 9 


Oct. 27 


Nov. 7 


Nov. 20 


Dec. 11 


Frost-resistant crops: 














Rye 


15.2 


11.8 


12.1 


14.1 


15.5 


16.0 


Oats 


15.1 


13.3 


12.3 


14.9 


13.9 


14.4 


Rape 


15.8 


12.8 


11.8 


14.4 


14.2 


14.0 


Field peas 


19.5 


15.8 


14.7 


17.2 


15.0 


15.6 


Average 


16.4 


13.4 


12.7 


15.2 


14.7 


15.0 


Frost-killed crops: 














Millet 


16.5 
17.3 


12.6 
15.1 


12.4 
13.8 


19.4 
20.0 


18.9 
19 6 


17.6 


Cane 


17.9 


Corn 


17.6 


13.8 


13.5 


18.7 


19.0 


19.7 


Average 


17.1 


13.8 


13.2 


19.4 


19.2 


18.4 


No crop: 




Few weeds 


20.0 
18.6 

19.3 


18.4 
17.8 

18.1 


20.3 

18.2 

19.3 


20.6 
19.1 

19.9 


19.8 
18.3 

19.1 


18.1 




18.5 


Average 


18.3 



Figure 28, also from Emerson, a graphic representation of the same 
figures, shows these effects even more strikingly. Both classes reduced 




Fig. 28. — Percentages of soil moisture in bare ground and under frost-killed and frost- 
resistant cover crops. {After Emerson^) 

soil moisture sharply in September and October, a very desirable effect 
when the need for ripening of wood is considered. Early in November, 



WINTER INJURY 281 

however, the frost-killed crops, no longer growing, ceased to draw on the 
moisture supply while, the frost-resistant crops kept the moisture content 
low. When it is recalled that Emerson's earlier work showed 19 dead 
trees and none uninjured out of 25 in soil with 15.2 per cent, moisture, as 
here under frost-resistant crops, while soil with 19.8 per cent., the nearest 
figure to that of the soil under frost-killed crops, showed three dead and 
12 uninjured, the importance of this difference is evident. The graph 
for the soil with no cover crop shows a somewhat higher moisture content 
in December than either class of cover crops but it also shows a high 
moisture content in September and October, suggesting a prolonged 
growing season and poor maturity in the tops. This is what actually 
occurred. Emerson's work emphasizes the importance of a water supply 
after maturity is attained. 

A plentiful supply of available water is an important factor deter- 
mining the recovery of plant tissues from the effects of low temperatures. 
Pantanelli has shown that the activity of the roots is of great importance 
in determining the recuperative power of the plant after the aerial parts 
have been exposed to low temperatures and that all those factors that 
reduce the absorbing capacity of the roots, such as insufficient aeration, 
salinity, alkalinity and the presence of toxic substances reduce the 
recuperative power of the plant. 

Windbreaks. — The relation to the orchard of shelter belts composed of 
hardy trees and shrubs has been the subject of much discussion, of some 
observation but of little precise study. ^Variations in local conditions 
of exposure to prevailing winds and in the character of these prevailing 
winds, as well as the topography of the orchards themselves, pre- 
clude the possibility of windbreaks being universally beneficial or injurious. 
Their efficacy, when properly placed, in cutting down the windfall 
loss from summer storms, is not a matter for discussion here. In 
the Michigan and New York fruit sections much of the advantage 
claimed for them is the protection they afford from those types of 
winter injury that are associated with drying out and they are set usually 
on a northern boundary of the orchard. In the north central states 
windbreaks seem to be planted more as protection against the hot drying 
winds of summer; hence, they are generally set on southerly boundaries. 

Effect of Wind Velocity. — Of quantitative data on windbreak effects, 
little is available. The increased snow deposit in places sheltered from 
the full sweep of the wind is a matter of common observation. After the 
snow has fallen the windbreak acts to preserve it. from evaporation by 
protecting it from the full force of the wind. Fernow 65 states that 
snow evaporates ten times as fast in warm wind (velocity not stated) 
as in calm air. Provided the snow accumulation is not great enough 
to injure the tops of young trees this effect must be beneficial since 
data to be introduced show the great power of snow in protecting roots 



282 



FUNDAMENTALS OF FRUIT PRODUCTION 



against freezing. How much the windbreak prevents the drying out 
of the tree tops during the high, desiccating cold winds of winter is a 
matter which with present data can be only conjectured. 

Certain experiments have shown that "with the temperature of the air at 
84 and a relative humidity of 50 per cent, evaporation with the wind blowing at 
5 miles an hour was 2.2 times greater than in the calm; at 10 miles 3.8; at 15 
miles 4.9; at 20 miles 5.7; at 25 miles 6.1 and at 30 miles per hour the wind would 
evaporate 6.3 times as much water as a calm atmosphere of the same temperature 
and humidity." 80 

Bates 15 found, in comparing wind movements in the open with those at a 
leeward point distant from the windbreak five times its height, that "a wind 
which reaches a velocity of 25 miles per hour in the open will, in the shelter of a 
good windbreak, have a velocity of . . . only 5 miles per hour." 

Combining these sets of figures, the evaporation in this case would 
be only 39 per cent, of that in the open. Figure 29, reproduced from 
Bates' study, shows the percentage of protection to increase with the 
wind velocity. 

100 
90 
80 

C 50 
£ 50 
*~> 40 
& 30 

20 

10 

0. 









' 










^^ 


OOr. , 






1 


^^corro„ 


Wonn o 




\ 




-Lk^u QF/r 




\ 








\ 


• 






V VJHI 


TF PINE BEJJL 























Wind Velocity in Open (miles per hour) 



20 



Fig. 29. — Wind at points five times the heights of windbreak to leeward, in terms of 
wind in open. {After Bates 59 ) 

Effect on Evaporation. — Card 31 in Nebraska determined the rates of evapo- 
ration at different distances from a windbreak 8 rods wide and 25 to 40 
feet high. Though these observations were made in summer, they are somewhat 
indicative of winter conditions and furthermore they have an important bearing 
on the state of trees as they approach dormancy. If the evaporation on the 
windward side of the windbreak during all the time that drying winds were 
blowing be represented by 100, then the evaporation at a point 12 rods distant 
on the leeward side would be proportionally 83 and at 3 rods distant it would be 
55. During a period of high though not particularly dry wind the respective 
rates were as 100 to 67 to 29. Numerous interesting studies of evaporation 
rates are reported by Bates, as shown in Table 25, arranged from his data. 

Effect on Soil Moisture. — The importance of soil moisture in relation 
to winter drought has been shown. For this reason, Card's determi- 
nations of soil moisture at varying distances on the leeward side of a wind- 



WINTER INJURY 



283 



Table 25. — Mean Efficiency of Windbreaks in Area of Greatest 
Protection (After Bates 16 ) 



Kind of windbreak 



(Area 12 times as wide as height of trees) 



Width, 
feet 



Height, 
feet 



Moisture saved at different 
velocities, per cent. 



10 



20 



Period of 
observation 



Cottonwood grove (underplanted) 

White pine belt 

Cottonwood row (natural density) 
Cottonwood belt (no low 

branches) 

Cottonwood row (reinforced with 

ash) 

Osage orange hedge (lower 

branches trimmed) 
Mulberry, single row 



100 



75 
20 
.50 



40 
23 
32 



23.9 
31.1 
12.3 

11.7 

12.8 
26.0 



31.9 
33.3 

18.6 

13.9 

20.2 
27.2 
28.7 



38.7 
35.8 
26.6 

15.5 

23.7 
27.2 



40. 1 
33.4 

17.0 

25.8 
27.5 



July, Sept. 

Nov. 

June, July, Aug. 

Aug., Sept. 

Sept. 

June, July, Aug. 

Aug. 



break are of particular interest. Table 26, arranged from his report 
of determinations made November 5, shows a difference well worth 
consideration, particularly as they were made at the approach of winter. 
Assuming, as Card does, that soil moisture up to 10 per cent, is not 
available for plants, the average available moisture up to a distance of 
about 7 rods was 2.55 per cent.; beyond that point it was 0.65 per cent. 

Table 26. — Soil Moisture at Varying Distances from a Windbreak 31 



Distance (rods) 


Percentage of moisture 


Available for plants 


1 


14.0 


4.0 


3 


12.6 


2.6 


5 


11.3 


1.3 


7 


12.3 


2.3 


9 


10.7 


0.7 


11 


10.5 


5 


13 


10.6 


0.6 


15 


10.8 


0.8 



The area protected by a windbreak is variable. It has been stated 
that in the Rhone valley each foot in the height of a windbreak protects 
plants for 11 feet to the leeward. 65 From rather general observations in 
Iowa and Nebraska it has been estimated that a rod of ground is sheltered 
for each foot in height of the windbreak, and other estimates state that a 
windbreak 25 feet in height will protect 10 rods of orchard. Bates 
found that the area extended on the average not more than 20 times the 
height of the windbreak; at this distance the wind velocities were found 
to be almost as great as on the windward side. Card's soil moisture 
determinations indicate that for this windbreak the effects were not 



284 FUNDAMENTALS OF FRUIT PRODUCTION 

evident beyond 7 rods. Unfortunately these figures were made in an 
open field and there is at present no means of stating just to what extent 
the orchard will protect itself at points beyond the sheltering effects of 
the windbreak, though observation indicates that it does to a considerable 
extent. Injury from cold drying winds in the 1903-1904 winter was 
found to be more severe in the outside rows of many orchards. 

INJURIES CHARACTERISTIC OF LATE WINTER CONDITIONS 

Primarily all winter injuries are induced by cold. This fact should 
be kept in view though for convenience the late winter injuries are treated 
as due to warm weather. It is not the heat that does the harm but cold 
weather, even in moderate degree, following warm weather. In one 
form or another, all fruit growing sections in temperate regions suffer 
through injuries proceeding from these causes. 

The Rest Period 

Discussion of the rest period at this point should not be taken to mean 
that it is regarded among the effects of temperature; it is considered here 
very briefly because of its relation to them. Periodicity of growth is 
found in plants wherever they are; equatorial regions with uniform 
temperatures present the phenomenon of plants in the resting stage while 
others are in growth. Sometimes on the same tree one branch is resting 
while others are growing. Other factors than temperature are undoubt- 
edly concerned with the inception and with the end of the rest period. 

The dormant season should not be confused with the rest period, 
though the two overlap more or less; in temperate regions the former may 
begin after — or before — and generally extends beyond, the latter. In 
the peach, for example, the rest period may begin to "break" in January 
though the temperatures prevailing may prolong the dormant season 
into April. The rest period is not a time of complete cessation of plant 
activities. The activities commonly recognized as growth are at a 
standstill, but other functions, undoubtedly of equal necessity to the 
plant, are active. The beginning and end are probably gradual processes. 

If an attempt is made to force peach trees into growth in a greenhouse 
during November or early December little success is attained; if the 
attempt is made in late December less difficulty is encountered while in 
January there would be still less difficulty. In the first instance the 
trees are in the rest period; in the second, the rest period is breaking. 
In the first case, no matter how favorable the environment, there is no 
response; in the second, the response is rapid whenever the environment 
is suitable. 

Chandler 36 shows an interesting parallelism between the percentage 
of buds killed in 1905-1906 and the percentage of buds of the same 
varieties that could be forced into development early in the following 



WINTER INJURY 



285 



winter. The data are summarized in Table 27, which is arranged from a 
more detailed statement in Chandler's report. The relation is close 
enough to indicate why a given variety, of the Persian type for example, 
may be tender in the south where its rest period is likely to be broken 
and still be hardy in the north where cold weather is constant, or why in 
the same orchard it may be hardy during a winter of steady and fairly 
severe cold and still be tender during a mild winter. 

Recent studies indicate some correlation, even in Minnesota, between 
hardiness and the intensity of the rest period in certain plums, as shown 
in Table 28. These suggest that the rest period may be more important 
in the north than it generally has been considered, though they do not 
explain observed differences in bud killing early in the winter. 

Table 27. — Percentage of Buds Starting Early and op Buds Killed 36 



Group 


Percentage of 
buds started 
Dec. 12, 1906 


Percentage of 

buds started by 

Dec. 22, 1906 


Percentage of 

buds killed in 

1905-1906 


Hill's Chili type 

Chinese Cling tvpe 


3.6 
0.0 

0.0 

0.0 

27.9 

12.6 


40.7 
13.0 

6.7 

8.7 

86.7 

65.7 


39.7 
51.2 


Chinese Cling, excluding Elberta, 

a hybrid 

Green Twig varieties 


44.3 

50.6 


Heath Cling type 


79 1 


Other Persians 


78.9 



Table 28. — Time Required for Blooming under Laboratory Conditions at 

Different Intervals During the Winter 

(After Strausbaugh 1 * 9 ) 





Stella (semi-hardy) 


Tonka (semi-hardy) 


Assiniboine (hardy) 


Date 
collected 














Date of 


Days 


Date of 


Days 


Date of 


Days 




bloom 


required 


bloom 


required 


bloom 


required 


Oct. 3... 


Oct. 17 


15 


Oct. 17 


15 


Did not bloom 




Nov. 8... 


Nov. 22 


15 


Nov. 22 


15 


Did not bloom 




Nov. 19... 


Dec. 4 


16 


Dec. 4 


16 


Did not bloom 




Jan. 24... 


Feb. 2 


10 


Feb. 2 


10 


Feb. 18 


26 


Feb. 6... 


Feb. 15 


10 


Feb. 15 


10 


Feb. 23 


18 


Feb. 21... 


Mar. 2 


11 


Mar. 2 


11 


Mar. 8 


17 


Feb. 28... 


Mar. 7 


9 


Mar. 7 


9 


Mar. 14 


16 


Mar. 5. . . 


| Mar. 13 


9 


Mar. 13 


9 


Mar. 19 


15 



Different plants appear to have rest periods of unequal length; in fact 
some, such as certain spiraeas, seem to have none. However, the rest 
period for each plant seems to be fairly constant provided no disturbing 



286 FUNDAMENTALS OF FRUIT PRODUCTION 

influence acts upon the plant. It follows, then, that the earlier the plant 
enters upon its period of rest the earlier the period is over. This is a 
matter of some practical import, as appears later. 

The rest period can be shortened, or broken, by various treatments. 
Etherization, light, wounding, desiccation, hot-water baths and exposure 
to freezing all bring it to an early end. For the forcing of certain flowers, 
such as lilacs, etherization is sometimes used; the greenhouse man who 
wishes to force fruits exposes the trees to cold. Northern greenhouses 
in Europe can force fruit and have it on the markets somewhat in advance 
of the greenhouse fruit crop from many more southern parts because the 
trees can be exposed to a freezing temperature earlier in the north and 
the rest period broken earlier. For the orchardist, however, the chief 
interest is in prolonging the rest period; this can be done in some cases, 
discussed later, by postponing its advent. In northern sections, though 
the temperatures are undoubtedly severe enough early in the winter to 
break the rest period, they are low enough to prolong dormancy and the 
rest period is relatively of less importance there. Farther south, where 
warm periods come during the winter, it is of much greater significance. 

The exact natures of the changes involved in the beginning and the end of the 
rest period are not known. A puzzling fact is mentioned by Schimper: A low 
temperature in the growing season will not have the same effect as in the dormant 
season; the change of starch to sugar in the potato accompanying cold in the 
winter is not duplicated in the summer. Since ordinary growing temperatures 
are without effect on the rest period, chemical changes appear not to be the con- 
trolling factors. Since time is a recognized factor a physical change is suggested. 
It seems significant that all processes known to shorten the rest period are known 
also to increase permeability. 

Injuries to Fruit Buds 

The killing of fruit buds which have started into activity is more 
evident in southern sections. Whitten 210 discusses winter killing of the 
peach in Missouri as of this nature. He states: "The growth of buds 
during warm weather in winter renders them very susceptible to injury 
from subsequent freezing. This is the most common cause of winter 
killing to peach buds in this state. Very often a warm spell as early as 
February causes peach buds to make considerable growth. If growth 
starts to any great extent the subsequent cold weather is almost sure to 
kill the buds." Chandler 38 states that "there has very seldom been a 
year when buds in the peach section of southern Missouri have not been 
started sufficiently by Feb. 1 to be killed by a temperature considerably 
higher than would be required to kill buds in northern Missouri, or 
certainly in Michigan, New York or New England on the same date." 

It is possible that occasionally the injury in these cases of warm 
weather followed by cold is due merely to the sudden drop in temperature. 



WINTER INJURY 



287 



Indeed, Chandler 38 cites convincing evidence to this effect: "In the 
year of 1901-1902 all of the buds were killed at the Missouri Experiment 
Station orchard by a temperature of — 23°F. on Dec. 20. In 1902- 
1903 practically all buds were killed by a temperature of — 15°F. on Feb. 
17. In 1903-1904 buds were killed on all varieties except General Lee, 
Chinese Cling, Thurber, Carman, Gold Drop, Triumph and Lewis by 
a temperature of — 14°F. on Jan. 29. During the winter of 1904-1905 
nearly all the buds were killed, yet practically all trees had a few left 
alive and Triumph and Lewis a fair crop following a temperature of 
-25°F. on Feb. 13. ... on Jan. 12, 1909, practically all the buds were 
killed except on the most hardy varieties by a temperature of — 11°F. In 
fact, fewer peaches were borne at Columbia following the winter of 1908- 
1909 than following the winter of 1904-1905 when the temperature fell 
to — 25°F. on Feb. 13. ... there was not more warm weather to start 
the buds preceding the freeze of Jan. 12, 1909, at Columbia . . than 
preceding the freeze of Feb. 13, 1905, at Columbia. 

"It would hardly seem possible that the buds in either case could 
have been started into slight growth preceding the freeze. Buds start 
very slowly even at high temperature early in January. . . . the low 
temperature of Jan. 12, 1909, came suddenly following high temperature 
while that of Feb. 13, 1905, came following 42 days of rather low tempera- 
ture. For 16 days the maximum temperature did not go above the 
freezing point. " 

Chandler suggests two possible reasons for buds surviving the colder 
temperature of the 1904-1905 winter: the long exposure to low tempera- 
ture which hardened them and the very slow falling of the temperatures. 

Changes in Water Content of Buds During Winter. — There is, how- 
ever, abundant evidence that development in peach buds during warm 
periods of the winter is frequently a contributing factor in winter injury. 
Investigations in Maryland show a progressive change which easily may 
be accelerated by pronounced warm weather." It seems significant that 



Table 29. — Water Content of Peach Fruit Buds 
(After Johnston") 



Date of sample 


Average green weight 
(grams) 


Average dry weight 
(grams) 


Ratio water con- 
tent to green 
weight 


Ratio water con- 
tent to dry weight 




Elberta 


Greens- 
boro 


Elberta 


Greens- 
boro 


Elberta 


Greens- 
boro 


Elberta 


Greens- 
boro 


Nov. 8 


0.124 
0.144 
0. 144 
0. 164 
0.327 
1.050 


0.121 
0.129 
0.123 
0.128 
0.220 
0.750 


0.073 
0.079 
0.082 
0.082 
0.115 
0.205 


0.073 
0.073 
0.075 
0.075 
0.092 
0.180 


0.41 
0.46 
0.43 
0.49 
0.65 
0.80 


0.40 
0.43 
0.38 
0.42 
0.58 
0.76 


0.69 
0.84 
0.76 
0.99 
1.85 
4. 12 


65 


Dec. 6 

Jan. 7 

Feb. 7 

Mar. 7 

Mar. 28 


0.76 
0.62 
0.71 
1.37 
3.17 



288 FUNDAMENTALS OF FRUIT PRODUCTION 

the more tender variety of the two studied shows this change in greater 
degree. 

Contributing Factors. — Roberts, 161 in Wisconsin, investigating blos- 
som bud killing in the sour cherry, concluded that suceptibility is in direct 
relation to the degree of advancement, the more advanced blossoms 
suffering most. He states: "The amount of injury is in relation to 
the degree of development of the blossom buds, which, in turn, is usually 
in [inverse] proportion to the amount of growth the tree is making." 
These conclusions were reached after microscopic investigation as well 
as field studies. 

The position of the hardiest buds was investigated by Chandler 36 
whose report follows, in part; . . . "the hardy buds are those borne at 
the base of the whips (last year's growth). ... at the base of the 
whips on trees not cut back only a slightly larger percentage of buds were 
killed than were killed at the tips of cut back trees. . . . Now it is 
possible to head back so severely that no fruit buds will be formed except 
at the outer end of the branches. This is especially true if the tree has 
a narrow dense head. ... If the tree be spreading in form, heading 
back is not so likely to cause the next season's wood to be in very long 
whips that either have branches at the basal nodes instead of fruit buds, 
or have the leaves at these basal nodes killed by the shade before fruit 
buds can be formed. This is true because the spreading heads would 
afford room for a larger number of whips to grow and obtain light, and 
the larger the number of nearly equal growing whips, other conditions 
of the tree being equal, the shorter necessarily will be the growth in 
each whip." Data are cited showing a loss of 60.2 per cent, of fruit 
buds on a large low-growing, spreading Oldmixon as compared with 
86.4 per cent, on a tree of the same variety making very large, upright 
growth and 90.8 per cent, on still another Oldmixon making small 
upright growth. 

Protective Measures. — Late entrance into the resting stage has been 
said above to cause a delay in breaking the rest period. This may be 
effected in a number of ways. 

Pruning. — One of the means of inducing late growth and late entrance 
into the resting period is pruning heavily enough to stimulate vigorous 
growth. Chandler 36 reports results of investigations in forcing twigs 
of a large number of peach varieties which he summarizes as follows : 

"Average per cent, started on trees making large growth 

(cut back) 20.5 

Average per cent, started on trees making small growth 

(not cut back) 31.2 

Number of varieties in which trees not cut back started first. .20 

Number of varieties in which trees cut back started first 3. 

Number in which both started about equally 4. 



WINTER INJURY 



289 



" . . . If we take the average of buds started on twigs taken 
December 22, or later, that is, when the resting period is nearly ended, we 
have ; — 

For trees making large growth (cut back) 28.3 per cent, started. 

For trees making smaller growth (not cut back) 48.6 per cent, started. 

"Taking only those varieties in which one tree had 60 per cent 
of the buds started, and therefore may be considered to have finished its 
resting period, we have as an average — 

On trees making large growth (cut back) 44.3 per cent, of the buds 
started; 

On trees making smaller growth (not cut back) 83.4 per cent, of the 
buds started." 

It is apparent that the more favorable the conditions become for 
breaking of the rest period the more evident becomes the restraining 
influence of late maturity. 

That this retardation of development by pruning actually results in 
lessening winter injury of the type under discussion is shown by numerous 
instances cited by Chandler. After a succession of warm days followed 
by a fall to — 3°F., which would hardly kill any considerable number of 
buds unless they had started into development, a count was made of 
dead buds on pruned and unpruned trees. Table 30, arranged from 
Chandler's data, shows one instance. Even more striking is his enumera- 
tion of results at Brandsville, Missouri, following the freeze of Mar. 16, 
1911, when 98.08 per cent, of the buds on unpruned trees were killed 
while only 81.9 per cent, were killed on the severely pruned trees. 38 The 

Table 30. — Buds Killed at — 3°F. on Pkuned and Unpruned Trees 38 

Per cent, killed 





Variety 








Pruned 


Unpruned 


Elberta 


48.5 
62.9 
30.0 
16.0 
23.9 

36.2 


67 8 


Oldmixon Free 


78 


Triumph 

Lewis 


59.1 

25 7 


Early Tillotson 

Average 


54.7 
59.8 



killing on the pruned trees seems high but 18.1 per cent, of peach buds 
may produce a full crop, as they did in this instance, while the unpruned 
trees bore only a few peaches. 

Fertilization and Cultivation. — Nitrogenous fertilizers, stimulating 
vegetative growth, have much the same effect as pruning, according to 



290 



FUNDAMENTALS OF FRUIT PRODUCTION 



Chandler. In one case, at Brandsville, Mar. 16, 1911, unfertilized trees 
lost 98.4 per cent, of their buds while trees fertilized with ammonium 
sulfate lost 77.6 per cent, and those which had received nitrate of soda 
lost 87.1 per cent. In one instance the fertilizer saved enough buds to 
make a full crop, in the other enough for a fair crop. 

Late cultivation has been reported to have the same results in 
retarding the rest period and increasing hardiness. 

Thinning. — Thinning has been observed to have beneficial effects 
on hardiness. Chandler 36 cites a case in which buds of certain varieties 
survived a winter that killed those of most varieties. These trees then 
bore a full crop but in the following winter their fruit buds succumbed 
while the varieties tender in the previous year survived. To secure 
experimental data the fruit on half of each of several heavily loaded trees 
was thinned with the results shown in Table 31. When the experiment 



Table 31. — Effect of Thinning Fruit on Hardiness of Buds 38 



Percentage of buds killed 



Variety 




Seedling 

Elberta Seedling 

Oldmixon Cling 

Poole's Favorite 

Poole's Favorite No. 2 

Average 



was repeated in 1908, 38 the effects of the freeze of Jan. 12, 1909, following 
weather such that all buds may be regarded as dormant at the time, were 
quite different, the unthinned limbs losing 92.5 and the thinned 93.2 
per cent, of their buds. Laboratory results are reported as follows: 
"These results suggest that thinning has its effect on the rest period 
rather than on the intrinsic hardiness of the buds. Where the tree is 
bent under a heavy load and under the strain of bearing a heavy crop, 
as when it is not thinned, the moisture supply probably being partially 
shut off, the same condition will prevail, at least to some extent, as when 
the trees are not cultivated; they will become dormant earlier and end 
their rest period earlier. Thus thinning, like heavy pruning and ferti- 
lizing with nitrogen can be expected to increase the hardiness of peach 
fruit buds only in climates like that from Central Missouri South, where 
there is likely to be weather warm enough to start the buds into growth 
before the effect of the rest period ends." 



WINTER INJURY 



291 



Whitewashing and Shading. — Sunlight is an important influence 
in forcing buds. 210 The spraying of peach trees with whitewash resulted 
in a reduction of heat absorption, with the effects on blossoming shown 
in Table 32, arranged from a similar table by Whitten. These data 

Table 32.— Blossoming Dates of Whitewashed Peach Trees 210 





First blossoms 


Full bloom 


Last blossoms 


Variety 


White- 
washed 


Not white- 
washed 


White- 
washed 


Not white- 
washed 


White- 
washed 


Not white- 
washed 


Heath Cling 

Wonderful 

Rivers' Early . . 
Silver Medal . . . 


Apr. 13 
Apr. 14 
Apr. 13 
Apr. 13 


Apr. 11 
Apr. 11 
Apr. 9 
Apr. 7 


Apr. 21 
Apr. 22 
Apr. — 
Apr. 18 


Apr. 18 
Apr. 18 
Apr. 21 
Apr. 13 


Apr. 29 
Apr. 29 
Apr. 29 
Apr. 28 


Apr. 27 
Apr. 25 
Apr. 27 
Apr. 21 



do not, however, show the full force of reduced sunlight absorption as its 
effectiveness would be greatest during the warm periods of winter 
while atmospheric temperatures are lower and when even slight develop- 
ment may result in winter-killing. Somewhat similar results have 
been obtained with plums in Ontario, but not with the apple, 116 which 
blossoms much later when the air temperature has greater influence 
in proportion to heat of insolation than it has earlier in the season. 
Even farther south, because of the difficulty in keeping trees well covered 
with whitewash and the consequent expense involved together with the 
ever-present possibility of conditions that will kill buds despite the 
covering, this method is little used. 

Board shelters have been found even. more efficacious than white- 
washing but again the expense involved precludes their use. 210 However, 
a choice tree or two can sometimes be located on the shady side of a 
building to good effect and sometimes a hill can be of advantage in secur- 
ing partial shade from the low midwinter sun for a good sized orchard. 

In General. — The peach has been used as illustrative matter here, 
because it has been studied the most thoroughly. More or less similar 
application may be made to Japanese plums, apricots, almonds and 
cherries. 

Finally it should be emphasized that the breaking of the rest period 
in the buds is entirely independent of the roots and that efforts to retard 
blossom development during warm periods in the winter by mulching the 
ground to keep it frozen or by spreading snow on the ground around the 
trees are absolutely wasted. Trees open their buds while the soil about 
the roots is still frozen or after they have been cut away from the roots. 
Time and again evidence to this effect has been presented and afterward 
the same useless effort repeated. The winter rest period of buds can be 
influenced through the roots during the growing season only. 



292 FUNDAMENTALS OF FRUIT PRODUCTION 

Attention must be called to the greater application of the principles 
just outlined the farther south the location and their diminished applica- 
bility northward. Wiegand 213 reported that in New York fruit buds 
did not grow from about Nov. 15 until about Mar. 1, when apple and 
apricot buds began a relatively rapid development culminating in open 
blossoms 8 and 7 weeks later respectively. Peach buds did not begin 
their spring growth until Mar. 23 and came into blossom with the apricots 
on Apr. 23. It appears from these observations that the cooler and 
shorter growing season in the north, though it stops growth earlier 
by the calendar, makes the peach buds less advanced at the onset of the 
dormant period and less easily started into growth, while the colder 
winters add to this effect. 

However, an interesting case is reported by Maynard 124 in Massachu- 
setts. Early in November, 1884, peach buds appeared fully matured. 
Following warm weather late in the month the stamens and pistils in- 
creased measurably in size and the bud scales loosened. The minimum 
temperature to Dec. 11 was 18°F.; at this time some buds had been killed, 
but the majority were unhurt and the petals had begun to take on color. 
Following a minimum of 10°F. on Dec. 19 and 20 all fruit buds were 
destroyed. 

Premature starting from the rest period is, however, a less common 
occurrence in northern peach regions. The very practices recommended 
for retarding it, if carried out too thoroughly in northern regions, though 
they might conceivably benefit the grower once in 20 seasons, would in 
the other 19 make his trees more liable to injury because immature and he 
would probably have damaged trees in 10 of these years. The southern 
grower guarding perhaps once against immaturity would suffer from pre- 
cocious bud development 10 times. Each grower must determine the 
danger more commonly met in his orchard and steer wide of this particular 
rock, hoping he will no more than scrape his keel on the other. At the 
same time the grower in "southern" regions may be on the northern 
limit for certain of the southern peach groups and thus in the same 
orchard he may have to contend with short rest period in one variety 
and with immaturity in another. 

Injuries to Vegetative Tissues 

Sunscald is the common name of a late winter injury likely to occur 
in the north as well as in the south. It is found on all types of fruit trees, 
on European chestnut and on various shade and forest trees. Very 
small trees are rarely troubled by winter sunscald and trees old enough 
to develop thick, scaly bark are less subject in the parts so protected. 
Attention is drawn to the injury by the dead and dry appearance of the 
bark on the southwest side of the trunk where the sun strikes strongest 
between noon and 2 o'clock. Sometimes this area is filled with a fer- 



WINTER INJURY 293 

merited fluid and the injury is called "sour sap." Later the bark may 
loosen and fall away leaving an exposed area of dead sap-wood. Many 
trees pruned to an open center are affected at the crotch or even high on 
the south side of those scaffold limbs that lean to the north. In this 
last position the sun's rays are received nearly at right angles and the 
injury there is in many cases very severe. 

The chief importance of this injury lies in its ultimate effects rather 
than in its immediate results. It leads at once, obviously, to partial 
obstruction of conduction of nutrient and food materials, but of greater 
moment is the exposure to fungi and borers and the resultant mechanical 
weakening of the tree. 

Distinguished from Summer Sunscald and Injuries Associated with 
Immaturity. — Distinction between this type and winter killing associated 
with immaturity on the one hand and between this type and summer 
sunscald on the other is sometimes difficult. In fact some writers have 
denied the existence of sunscald and some have maintained that summer 
heat never kills bark. Evidence showing that bark is sometimes killed 
by high temperatures is easily gathered. Fisher 68 quotes Vonhausen as 
rinding, between the sapwood and bark, a temperature of 120°F. when the 
air temperature was 91°F., while in Bavaria, Hartig observed a tempera- 
ture of 131°F. between the bark and sapwood of some isolated 80-year 
old spruce trees. This is a lethal temperature for leaves and herbaceous 
shoots and is presumably so for cambium cells. In forests when an open- 
ing is made, the standing trees on the north side of the clearing in many 
cases show the sunscald high on the south side of their trunks. Young 
apple trees set late in the spring in sandy soil and headed back so they 
had little protecting top, have been observed even in New Hampshire, 
to show severe sunscald by midsummer. 

Caution should be observed, however, in attributing all injuries on the 
southwest side of the tree to late winter sunscald. Balmer 12 describing 
the effects of a November freeze in Washington mentions that trees with 
high trunks, leaning from the afternoon sun, suffered notably. In several 
cases the bark on the southwest side of the trunks split open. Investiga- 
tors seem to have overlooked the possible effects of radiation in this 
connection. It is shown under Frost Injury that the temperature 
near the soil on a frosty night may be 10° or more lower than that recorded 
by a sheltered thermometer near by. An October temperature of 20°F. 
is not uncommon; with suitable radiation conditions the temperature 
near the soil, if 10° lower, would be 10°F., low enough to cause consider- 
able injury to immature tissues. Since somewhat lower temperatures 
occur over sod under these conditions than over cultivated ground the 
occurrence of "sunscald" in sod orchards need not be surprising. Injury 
of this kind is obviously associated with immaturity. Therefore it is not 
safe to consider sunscald altogether a late winter injury. 



294 FUNDAMENTALS OF FRUIT PRODUCTION 

Moisture and Temperature Conditions in the Affected Parts. — The 

winter sunscald, however, is much more common. It is not induced by- 
simple insolation but by interacting effects of heat and cold. This is 
quite evidently the malady described by Downing 54 in 1846 as "frozen 
sap blight" and rather confused with pear blight by many of the early 
American pomological writers. The description by Downing clearly 
indicates this form, as he includes Ailanthus, Spanish chestnut and 
catalpa among the plants affected. He attributed the trouble to sudden 
thawing and proposed as a remedy shading the south side of the trunk 
and whitewashing. Somewhat later he recorded that on Dec. 19, 1846, 
a bright mild day, with snow on the ground, a naked theremometer regis- 
tered 97°F. while one with a whitewashed bulb registered 79°F. 55 Various 
suggestions as to the way sunscald is brought about have been made, in- 
cluding rapid thawing, increased flow of sap followed by freezing so that 
the bark is pushed off, breaking of the rest period in the warmed area and 
alternate freezing and thawing. Muller-Thurgau 69 found in March a 
water content of 53.8 per cent, in the bark on the south side of a plum 
tree and 48.5 per cent, on the north while the bark of a tree wrapped 
with rushes showed moisture percentages of 51.5 and 51.3 on the south 
and north sides respectively. He considered these figures to corroborate 
the suggestion that a localized breaking of the rest period subjected the 
affected areas to injury from subsequent cold. 

The most extensive investigation on this phase of winter killing is 
that of Mix. 135 Particular attention was given to the cambium since 
this tissue suffers severe injury "and without injury to the cambium and 
outermost xylem the bark would not separate from the wood." Obser- 
vations of temperature under the bark on the northeast and southwest 
sides of apple trunks showed no significant differences on cloudy days but 
marked variations on bright days, demonstrating the warming effect of 
the sun's rays. Tables 33 and 34 are selected from data reported by 
Mix from these observations and are representative of his more extended 
figures. The temperatures for Mar. 10 are worthy of special attention, 
being 32°F. on the northeast side and 69°F. on the southwest side at the 
same time. On Feb. 10, Mix observed on the southwest side of one tree 
a fall from 59° to 27°F. between 2 o'clock and 9, the air temperature 
dropping from 28° to 19° F. in the same time, while on the northeast side 
the temperature fell from 25° to 19°F. The temperature of the southwest 
side dropped 32°F. while that of the northeast side fell 6°F. On another 
tree the temperature on the southwest side fell between 5 o'clock and 6 
(sunset at 5:30) from —0.3° to — 14.4°C. while on the northeast side it 
dropped from —9.4° to — 18.3°C. This, it should be emphasized, was in 
1 hour. By morning the temperatures on both sides were frequently 
observed to be approximately equal. The southwest side of a tree trunk 
is evidently subject to wider fluctuations in temperature and to more 



WINTER INJURY 



295 



Table 33. — Tree Temperatures on Cloudy Days 

(After Mix 135 ) 







Southwest 


Northeast 




Date 


Hour 


side, 

degrees 

Centigrade 


side, 

degrees 

Centigrade 


Air, degrees 
Centigrade 


Jan. 15 


11:00 


-6.9 


-7.5 


-5.5 


Jan. 16 


1 


30 


3.3 


2.8 


2.6 


Jan. 17 


1 


30 


-1.9 


-3.0 


-3.9 


Jan. 19 


1 


00 


-3.9 


-3.9 


-2.5 


Jan. 20 


11 


40 


0.0 


0.0 


1.1 


Jan. 21 


1 


00 


0.0 


0.0 


-2.2 


Jan. 23 


1 

1 


10 
10 


-2.2 
-0.5 


-2.2 
-0.5 


0.0 


Jan. 24 


4.4 



Table 34. — Tree Temperatures on Sunny Days 

(Data from same tree as Table 33) 

(After Mix 1 ™) 



Date 


Hour 


Southwest 

side, 

degrees 

Centigrade 


Northeast 

side, 

degrees 

Centigrade 


Air, degrees 
Centigrade 


Jan. 14 

Jan. 26 

Feb. 2 

Feb. 3 

Feb. 4 


3:00 
3:25 
1:30 
1:35 
1:05 
2:10 

12:50 
1:00 
2:50 
1:00 
1:00 

12:55 

11:00 
1:30 

12:50 
1:15 
1:00 


-2.8 

1.1 

* 12.2 

15.0 

12.8 

-0.5 

-4.4 

-6.4 

3.9 

-6.4 

-2/8 

1.7 

-1.9 

20.5 

15.0 

12.2 

11.1 


-12.2 

-2.8 

-1.1 

2.8 

0.8 

-4.4 

-9.4 

-15.0 

-9.4 

-11.4 

-16.1 

-9.7 

-10.0 

0.0 

-3.3 

1.7 

5.0 


-12.2 

-1.4 

0.5 

9.4 

1.6 


Feb. 8 


-6.7 


Feb. 9 

Feb. 13 


-8.3 
-11.7 


Feb. 15 


-12.2 


Feb. 23 


-14.4 


Feb. 24 




Feb. 25 


-5.6 


Feb. 26 




Mar. 10 


1.1 


Mar. 12 


-4.4 


Mar. 24 


3.9 


Mar. 25 


8.9 



sudden falling of temperature after the sun's heat is withdrawn at 
sunset. Even more striking temperature differences may occur occasion- 
ally. In fact Mix records a temperature of 92°F. on the southwest side 
on Feb. 20, while the temperature on the northeast side was 35°F. 



296 



FUNDAMENTALS OF FRUIT PRODUCTION 



The effect of snow in relation to sunscald seems to have escaped the 
attention of writers on this subject. Sunlight striking snow is to a large 
extent reflected and a late winter snow is bound to have no little influence 
in intensifying the heating on the southwest side of tree trunks. If, 
as frequently happens in late winter in northern latitudes, a snowfall dur- 
ing the night is followed by a clear warm day and a night of considerable 
cold the change in temperature of the southwest side must be considerable 
and abrupt. 

Rapid freezing, especially during the first part of the temperature fall 
has been shown by Chandler 38 to cause killing at a relatively high point. 
These are the very conditions just recorded and seem adequate to explain 
killing by sunscald without any assumption that growth has started. 
Artificial freezings accompanied by microscopic examination of tissues 
made by Mix showed no difference in hardiness on either side when frozen 
under identical conditions. Rapid freezing killed at — 20°C. while 
slow freezing caused no injury at — 28°C. As spring advances these 
tissues become less hardy, but equally on all sides of the trunk. The 
conclusion seems inevitable, therefore, that it is rapid freezing after sun- 
down that causes winter sunscald. 

Preventive Measures. — Prevention of the rapid fall is best effected by 
keeping the day temperature down. Anything that will shade the trunk, 
as a stake or a bundle of corn stalks, will do this well. Whitewash also, 
because of its low heat absorption, may be used to advantage. 

Table 35. — Temperatures of Whitewashed, Tarred and Untreated Trees 13 





Air, degrees 
Centigrade 


Untreated Whitewashed Tarred 


Date 


Northeast, 
degrees 
Centi- 
grade 


South- 
west, 
degrees 
Centi- 
grade 


Northeast, 
degrees 
Centi- 
grade 


South- 
west, 
degrees 
Centi- 
grade 


Northeast, 
degrees 
Centi- 
grade 


South- 
west, 
degrees 
Centi- 
grade 


Jan. 15 

Jan. 30 

Feb. 4 

Feb. 10 

Feb. 19 

Feb. 20 

Average 


3.9 
-5.6 
0.0 
-1.7 
3.9 
6.1 
1.1 


1.7 
-8.3 
-3.3 
-3.9 
-1.7 

0.0 
-2.6 


11.1 

-4.4 
7.2 
15.0 
17.2 
21.7 
11.3 


0.6 

-S.9 
-4.1 
-6.7 
-2.2 
-0.6 
-3.2 


2.2 

-2.8 

1.1 

-0.6 
5.0 
6.1 
1.8 


3.3 
-4.9 
-0.6 
-1.1 

0.0 

1.7 

-0.3 


20.5 
13.9 

17.8 
29.0 
31.1 
33.3 
24.3 



Table 35, arranged from data reported by Mix, shows the sharp 
contrast in sunny side temperatures between a whitewashed and an 
untreated tree, a difference that becomes more marked as the tempera- 
tures go higher. The difference appears considerable enough to save 
treated trees from sunscald in many cases. The same table suggests 
also a reason why gas tar, occasionally applied as a borer repellant, is 
said frequently to kill trees. The difference between the temperatures 



WINTER INJURY 



297 



under whitewash and under tar is due apparently to the respective heat 
absorptive powers of white and black colors, as their minimum early 
morning temperatures were practically the same. 

INJURIES DUE TO SUDDEN COLD 

Though some types of injury already discussed as associated with 
immaturity of tissue might be considered to belong in the category of 
injuries due to sudden cold, they may be classed more correctly as due to 
untimely cold. Here, too, probably belongs the type known as winter 
sunscald which is discussed under late winter injuries but the present 
section is limited in its application to injuries occasioned by a sudden 
change from moderate cold to intense cold. 

General Effects. — Chandler 38 has been quoted earlier as reporting 
greater injury to plant tissue attendant upon sudden lowering of 
temperature. His statement, however, should be reproduced here : " The 
rate of temperature fall is very important indeed, especially in case of 
winter buds. In fact, apple buds can be frozen in a chamber surrounded 
by salt and ice rapidly enough so that practically all of them will be killed 
at a temperature of 0°F., or slightly below, while it is well known that 
they may go through a temperature of 20 to 30°F. below zero with but 
slight injury where the temperature fall is not so rapid. . . . the 
killing temperature of rapidly frozen twigs was 4.5° higher than those of 
the more slowly frozen twigs and even then the buds of the rapidly 
frozen twigs killed the worst." Table 36, chosen from several reported 
by Chandler, shows the difference vividly. 

Table 36. — Effect of Slow and Rapid Temperature Fall on Cherry Fruit 

Buds 38 



Variety 


Manner of freezing 


Date 


Number 

of 

buds 


Percent- 
age 
killed 


Montmorency 

Montmorency 

Early Richmond 

Early Richmond 


Slowly to -20°C. 
Rapidly to -20°C. 
Slowly to -20°C. 
Rapidly to -20°C. 


Mar. 2 
Feb. 29 
Mar. 9 

Mar. 14 


163 
130 

297 
263 


3.0 
96.0 

5.0 
98.0 



However, it should be remembered that Chandler found also a rapid 
fall to — 12°C. more injurious than a rapid fall from — 12°C. to the 
killing temperature. This is shown strikingly in Table 37, adapted from 
a table by Chandler. 

No data bearing on this matter drawn from field observations are 
available. Fortunately, as Chandler states, "In this investigation it 
was not possible to cause the temperature to fall more slowly than the 
most rapid fall to be observed naturally in the climate of this station 



298 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 37. — Effect of Rapid Fall Early and Late in the Freezing 



Variety 


Manner of freezing 


Date 


Number 
of buds 


Percent- 
age 
killed 


Elberta peach 

Elberta peach 


Slow to -12°; fast 

-12° to -16° 
Fast to -12°; slow 

-12° to -16° 
Slow to -17.5° 
Fast to -16.0° 
Fast to -12°; slow 

to -20° 
Slow to —12°; fast 

to -20° 
Fast to -20° 
Slow to -20° 


Dec. 20 

Dec. 20 

Dec. 20 
Dec. 8 
Feb. 24 

Feb. 27 

Feb. 27 
Mar. 2 


135 

77 

129 
135 
142 

136 

130 
163 


3.7 
71 4 


Elberta peach 


6.2 


Elberta peach 


98.5 


Montmorencv cherry 

Montmorency cherry 

Montmorency cherry 

Montmorency cherry 


75.0 

15.4 

96.0 
3.0 



(Missouri)." Hence, the "slow" of Tables 36 and 37 is the "fast" of 
nature. However, it seems quite possible that certain "warm spots" 
in an orchard may heat considerably during a clear, cold day only to 
have a very rapid drop in temperature following sunset and that some 
of the injury attributed to buds "starting growth" during winter is in 
reality due to a sudden and considerable drop of this kind. Nevertheless, 
in a large number of cases when wholesale destruction of fruit buds occurs 
it can be traced to some other cause. 

Trunk Splitting. — Trunk splitting is much more common in forest 
and shade trees and most of the literature on this type of injury deals 
with these trees. Nevertheless, it is by no means unknown in fruit 
trees; instances are on record of fruit trees splitting through the trunk. 192 

Close measurements in Europe have shown that temperatures under 
the freezing point induce a contraction in the trunks of various forest 
trees which with long continued freezing reaches the magnitude of an 
annual ring. 70 Deciduous trees react much more readily than evergreen. 
The generally accepted view is that a rapid fall of temperature induces 
a considerable contraction of the bark and outer wood while the inner 
wood, still at a much higher temperature, does not shrink equally; 
hence the splitting. The cracks start generally at the bark and proceed 
radially toward the center of the tree or even beyond. Objection has 
been raised that clefts extending beyond the center could not be caused 
in this way but if it be assumed that the center of the tree is already 
frozen, those who have cut frozen wood and know how easily it splits 
will have little difficulty in believing that an initial cracking at the 
periphery may be transmitted beyond the center because of the glassy 
nature of frozen wood and the pull of the contracting bark. 



WINTER INJURY 299 

Wind may, as has been suggested, 82 be associated with this type of 
injury under certain circumstances but there can be no doubt whatever 
that splitting occurs on absolutely still nights, the sharp, rifle-like 
report accompanying the fissure being very noticeable under such con- 
ditions. Fisher 67 discusses the subject at some length. He reports that 
most frost cracks occur in cold weather between midnight and morning 
and may close again with rising temperature; further, that sometimes an 
internal frost crack occurs, the sap-wood rending while the bark holds 
intact. Hardwoods with large medullary rays are most liable to this 
injury, oak, beech, walnut, elm, ash and sweet chestnut being mentioned 
as specially susceptible in Europe. 

The cracks are said to occur most frequently in the lower part of the 
trunk, especially where growth is uneven, as near roots, at knots or where 
the stem is eccentric. The south side, the region of most vigorous cir- 
cumferential growth, suffers most, according to Fisher. Large old trees 
suffer more than young because under conditions inducing this injury 
there is in the old trees a greater difference in temperature between center 
and periphery. Late winter, when the sap has begun to flow, is said to be 
the most favorable time for developments of this kind. Under normal 
conditions these cracks close with a rise in temperature and the tissues 
in time grow together; this spot is weaker however and subject to a 
recurrence of the injury. Repeated splitting and healing may give rise 
to a lipped callus. 

Observations in America agree generally with Fisher's, adding 
the maple to the list of subject trees and finding perhaps more crack- 
ing on long, straight-grained, clear boles. Indeed it seems that the two 
chief reasons for the comparative resistance of fruit trees lie in their 
being low headed, with short areas of trunk free from branches and in 
their smaller trunks. Under cultivation they probably do not mature as 
early as forest trees and the sappy growth of young trees may be injured 
in early winter in contrast with late winter for forest trees. It is stated 
that fruit trees growing late and entering the winter with wood not 
thoroughly ripened are most subject to frost cracks in Colorado. 52 

On apple limbs an injury similiar in appearance and likely to be 
confused with this type, sometimes occurs when there is one sided develop- 
ment of the limb so that a heavy load of fruit is borne on one side un- 
balanced by any considerable load on the other side, resulting in a fracture 
in a vertical plane. Occasionally after a nearly horizontal limb is headed 
back to a large branch ascending at about 45° a heavy load on the ascend- 
ing branch will cause a splitting of the upper part of the limb from the 
lower, the fracture being in this case horizontal. These injuries obvi- 
ously occur near harvest and should be differentiated from the true 
"frost cracks" without difficulty. 

The reverse of the conditions described in connection with radial 



300 FUNDAMENTALS OF FRUIT PRODUCTION 

clefts, that is to say, the sudden warming of the outer layers of the trunk 
while the inside is still cold, is said to produce a different kind of injury, 
known to foresters as a "cup-shake." Here the cleavage instead of 
being in a radial direction is along an annual ring, involving a smaller or 
greater amount of the circumference. This form may possibly occur in 
fruit trees but in most cases of separation along annual rings in such 
plants the injury may be traced to direct killing just inside the cambium, 
discussed under Black Heart. Even under natural conditions the cup- 
shake is far less common than the frost crack. 

In connection with trunk splitting, the splitting of the bark while the 
wood remains intact should be mentioned. As already indicated this is 
generally in immature tissues, produced possibly at times by the same 
conditions that induce trunk splitting but more frequently by the con- 
ditions commonly associated with crown rot and crotch injury. It 
should be understood, also, that splitting of the wood sometimes seems 
to be associated to some extent with immaturity 12 and it may possibly, 
as for example, when it occurs during protracted and intense cold, be due 
to drying out. 

Summary. — Winter injury takes many different aspects, 10 more or 
less distinct forms being considered in this discussion. Many different 
environmental conditions are associated with winter injury, though for 
convenience these may be grouped in three classes : (1) conditions encour- 
aging immaturity of tissues, (2) conditions leading to winter drought, 
(3) conditions leading to premature quickening in late winter and early 
spring. Certain sections or regions are particularly subject to extremes 
of one kind or another. 

Injuries associated with immaturity are especially common in the more 
humid sections with short growing seasons. Plants adapted to com- 
paratively long growing seasons when taken to sections with shorter 
growing seasons are particularly subject to injuries of this character. 
"Second growth" is likely to be immature and subject to winter injury. 
Cultural practices which encourage late vegetative growth should be 
avoided in regions where immaturity is a frequent problem. Crown 
injury and crotch injury are in most cases associated with immaturity of 
tissues at the affected points. Wind and variation in temperature 
between different sides of the limb or trunk may be contributing factors. 
Treatment for these localized injuries should be both preventive and 
remedial. 

Injuries due to winter drought are especially common in sections 
like the Dakotas and Wyoming where winter precipitation is low, the 
snow covering scanty and the evaporating power of the air high. The 
tissues are desiccated by the cold dry winds and recovery of turgidity 
is difficult or impossible because of low soil moisture, deep soil freezing 
and the inability of the conducting system to function while frozen. 



WINTER INJURY 301 

Protective measures include the use of winter irrigation, thorough 
cultivation, frost-killed cover crops and windbreaks or shelter belts. 

Many cases of injury from cold during late winter are associated 
with a breaking of the rest period, resulting in some resumption of growth 
and an accompanying decrease in resistance to low temperatures. They 
are brought on by periods of mild weather during late winter. Fruit 
buds particularly are susceptible to injury from this cause. Buds in 
certain positions are especially subject to this form of injury. The ending 
of the rest period in midwinter or spring is related to some extent to the 
time of its inception in the fall. Consequently factors or practices 
which delay its beginning tend to protect against the forms of winter 
injury incident to its breaking. Among such practices may be mentioned : 
Moderately late cultivation, reasonably heavy pruning, applications of 
nitrogenous fertilizers and thinning. The end of the dormant period may 
be delayed somewhat by whitewashing and shading, which reduce heat 
absorption. 

Most sunscald is attributable to extreme and rapid fluctuations 
in temperature of the affected tissues. Injuries similar in appearance 
sometimes are caused by midsummer heat or they may be associated 
with immaturity coupled with low temperature. 

In general, rapid decreases in temperature are more damaging than 
more gradual decreases to the same or even to a lower point. A special 
form of injury due to very rapid temperature decline is trunk splitting 
or frost crack. 



CHAPTER XVII 
WINTER INJURY TO THE ROOTS 

Root killing is very common in sections where winter precipitation 
is light and it is rather common in humid sections where it is not always 
recognized. It may occur, regardless of precipitation, at any point 
where the soil freezes at all deeply (see Table 38) ; it is characteristically 
associated with light and dry soils and with scanty snow cover. If 
no part other than the roots is injured the tree may start growth in the 
normal way, sending out vegetative shoots and blossoms and perhaps 
even setting fruit ; some time in the summer, usually with the first warm, 
dry weather, it dies. Felled trees will sometimes start growth in a 
comparable manner. If only a part of the roots have been injured, 
the effect is quite likely to be a slowing in top growth. As the damage 
is below ground, it escapes ordinary observation and the slow growth 
of the tree may seem quite inexplicable. This condition may last for 
several years or until the balance between root and top is more nearly 
restored. 

Soil Temperatures in Winter. — For a thorough understanding of the 
nature of root killing and of the conditions associated with it, some 
knowledge of soil conditions during the winter and of the distribution 
of roots in the soil is necessary. Table 39, taken from a report covering 
12 years of soil temperature observations at Lincoln, Neb., 190 shows 
quantitatively the effect of depth on soil temperatures. 



Table 38. — Mean Soil Temperatures at 6 Inches 19 
(Degrees Fahrenheit) 





December 


January 


February 


March 


Pennsylvania 


34.9 


32.0 


31.4 


32.9 


Idaho 


35.2 


32.1 


32.1 


32.9 


Minnesota 




23.0 


21.0 


38.0 


Wyoming 


24.1 


22.2 


22.7 


31.0 


Nebraska 


32.0 


28.6 


27.8 


36.6 


Michigan 


33.8 


32.0 


32.0 


33.5 


Woburn, England 


39.5 


39.0 


39.1 


39.9 


Colorado 


34.0 


27.7 


30.4 


36.3 


Illinois 


34.9 


32.7 


31.5 


39.3 


Alabama 


57.0 


56.1 


57.1 


53.4 



302 



WINTER INJURY TO THE ROOTS 



303 



The Pennsylvania figures are for State College, 1892-1896 inclusive; Idaho, 
for Moscow, 1903-1904 (Idaho Exp. Sta. Bui. 49); Minnesota, 1889 (a mild 
winter); Wyoming, averages for Laramie, 1895, 1898, 1899; Nebraska, from 
Table 39; Michigan, selected as typical, from Mich. Agr. Exp. Sta., Tech. Bui. 
26, p. 104; Woburn, England, 2d Rept, Woburn Experiment Farms (1900); 
Colorado, Fort Collins; Illinois (Urbana), (1897-1916); from Bui. 208, 111. Agr. 
Exp. Sta. ; Alabama, from Ala. Agr. Exp. Sta. Bui. 10. 

Table 40 is arranged from the same source and is introduced to 
show absolute minima at several depths, over a series of years. 



Table 39. — Average Soil Temperatures at Lincoln, Neb. 190 
(Degrees Fahrenheit) 



Depth 


January 


February 


March 


April 


May 


June 


Air 


25.2 
28.6 
31.2 
35.4 
38.5 


24.2 
27.8 
30.2 
33.5 
35.5 


35.8 
36.6 
35.4 
35.4 
35.8 


52.1 
53.3 
49.3 
45.6 

43.8 


61.9 
65.1 
60.7 
56.2 
53.5 


71 




75.7 




69.9 




64.6 




61.3 



Depth 


July 


August 


September 


October 


November 


December 




76.0 
81.6 
75.7 
70.2 
67.4 


74.5 
80.1 
75.7 
72.2 
69.8 


67.6 
72.0 
69.2 
68.7 
67.6 


55.5 
57.8 
57.8 
60.0 
61.6 


38.7 
41.5 
44.7 
49.2 
52.2 


28.3 
32.0 


12 inches 

36 inches 


35.2 
40. 1 
43.3 



Table 40. — Minimum Soil Temperatures at Lincoln, Neb. 190 
(Degrees Fahrenheit) 



Winter 


6 inches 


12 inches 


24 inches 


36 inches 


1893-1894 


19.6 


24.5 


30.2 


34.2 


1894-1895 


14.9 


22.9* 


29.2* 


29.8 


1895-1896 


18.0 


27.4 


35.5 


38.0 


1896-1897 


22.0 


27.0 


33.0 


35.1 


1897-1898 


20.0 


26.5 


34.5 


36.5 


1898-1899 


7.0 


13.5 


24 


30.5 


1899-1900 


22.0 


28.0 


33.0 


35.0 


1900-1901 


24.0 


28.0 


34.0 


36.0 


1901-1902 


19.0 


27.0 


33.0 


35.0 



Data incomplete. 



The maximum depth of frost penetration at the same point has been 
reported as detailed in Table 41. Recently, however, it has been shown 



304 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 41. — Maximum Depth of Frost Penetration at Lincoln, Neb. 15 



Date 


Depth, 
inches 


Date 


Depth, 
inches 


Mar. 9, 1891 

Jan. 19, 1892 

Feb. 12, 1893 


30.9 

21.9 

32.2 

29.0 

36.0* 

18.4 


Jan. 19, 1897 

Feb. 8, 1898 

Feb. 10 to Mar. 28, 1899 

Feb. 29, 1900 

Feb. 12, 1901 

Feb. 9, 1902 


21.2 
16.8 
36.0 


Feb. 27, 1894 


21.6 


Feb. 7-27, 1895 


20.0 


Jan. 4, 1896 


21.6 



* Not recorded to maximum penetration. 

that soil does not freeze until it is cooled several degrees below 32°F. 25 
Consequently since these figures were based on the assumption of freezing 
at 32° the actual frost penetration was not so great as is indicated. 

Critical Temperatures for Tree Roots. — In the section on Water 
Relations the extent and the depth of some fruit tree root systems are 
indicated. The data there given indicate that in the majority of fruit 
growing regions by far the greater part of the feeding roots is in the 
surface foot of soil. 

The finer roots of beech, oak and ash, trees that are considered 
at least fairly hardy, die at temperatures between 8.6° to 3.2°F. 197 and the 
roots of other hardy plants are reported killed at temperatures from 
14° to 5°F. 38 Working with apple roots, under laboratory conditions, 
Chandler found that "the killing temperature varies from — 3°C. in 
summer to about -12°C. [26.6°F. to 10.4°F.] in late winter with rather 
rapid freezing." He remarks further, "They are still very tender in 
autumn when tissue above ground has begun to increase rapidly in hardi- 
ness ... as the roots extend away from the crown they become more 
and more tender and apparently this tenderness is greater on those roots 
that extend downward into the soil." It may, then, be concluded that 
the roots of most plants are more tender, at a given temperature, than the 
parts above ground. Parenthetically, though Chandler's statement 
as to increasing tenderness with increasing distance from the crown may 
be accepted, it should be understood that root killing is frequently 
observed at or near the crown and not elsewhere, probably because this 
part is nearest the top soil and therefore exposed to colder temperatures, 
as shown in Table 39. 

Carrick 35 found a marked difference in tenderness of roots at different seasons 
in New York. "The material frozen in October and November," he states, 
"shows a marked tenderness compared with roots tested in February and March. 
The period of maximum resistance seems to end somewhat before the last of 
March, tho the date would, of course, vary with the conditions affecting 
after-ripening and possibly also with the variety . . . This range of hardiness 
indicates a difference in resistance of between 3 and 4 Centigrade degrees. 



WINTER INJURY TO THE ROOTS 305 

These seasonal differences obtain, not only in the apple seedlings, but in all the 
roots reported in this paper." 

Another interesting factor in root injury is reported by Carrick. He finds 
that, "the resistance is in direct proportion to the diameter of the root," and 
suggests that this fact accounts for the occasional observation in laboratory 
freezings of root killing at the tips when the roots near the crown are uninjured. 

A study of Table 38, with the killing temperatures given above in 
mind, shows that the average soil temperatures in the recognized fruit 
growing sections noted are substantially above the danger point and 
suggests one reason why fruit growing in certain other sections requires 
some special precautions. Attention is due, further, to the consideration 
that these are average figures in which fluctuations to lower points are 
submerged. In Table 40 the actual seasonal minimum temperatures at 
one point are segregated. It is particularly significant that the winter of 
1898-1899, when the soil temperature at Lincoln, Neb., reached 7°F., was 
the winter characterized by an extreme amount of root killing in Iowa, 51 
Wisconsin 76 and Ontario. 115 

Factors Influencing Frost Penetration. — Temperature alone, or air 
temperature alone certainly, is not the sole controlling factor in root 
killing. A temperature of — 20°F. maintained for several days has 
caused extensive root killing in Ontario. 50 Goff 76 in an interesting survey 
of an extensive area involved in the freeze of February, 1899, found little 
damage in several regions where the unofficial temperatures went as low 
as — 50° or even — 52°F., though in no case where root killing occurred 
had the temperature gone below — 36°F. A report from Waukee, Iowa, 
indicated root killing with a minimum of — 24°F. ; other localities suffered 
severely at - 23°F. 

Protection Afforded by Snow. — The principal difference lay in the 
fact that in some sections snow lay on the ground while in others there 
was none. Goff's analysis showed 34 localities with more or less snow 
at the time of the freeze; of these, 20 reported definitely that the chief 
injury was in the tops, three reported roots and tops equally damaged, 
while in one there was more injury to roots than to tops in apples but 
more in the tops of cherries and plums than in the roots. Fifty-seven 
localities were without snow at the time of the freeze; definite statements 
of comparative injury indicated 43 cases where the principal damage was 
in the roots, 3 placed it in the tops and 1 reported roots and tops 
equally damaged. 

Similar testimonials concerning the value of a snow covering are 
common in pomological literature. Quantitative data applicable here 
are given by Bouyoucos. 23 Table 42, arranged from his figures taken at a 
depth of 3 inches, shows the temperature differences between ground 
without snow, ground under compacted snow, under uncompacted snow 
and under vegetation plus compacted snow. 

20 



306 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 42. — Effect of Snow Cover on Soil Temperature, January, 1915 28 

(Degrees Fahrenheit) 





My average 




Maximum 


-minimum 


Air 


Mon 


Bare 


Snow, 
compact 


Uncom- 
pact 


Uncom- 

pact + 

vegetation 


Maxi- 
mum 


Mini- 
mum 


Average 






28.79 

24.95 

3.84 


29.65 

28.66 

0.99 


31.51 

31. 11 

0.40 


34.82 
34.55 

0.27 


27.96 


13.80 








20.64 








Jan. 6, <. 


maximum 


32.30 


32.00 


32.00 


35.70 








minimum 


32. 10 


31.80 


32.00 


35.50 


39.00 


33.00 


36.00 


Jan. 29, < 


maximum 


20.00 


22.30 


29.60 


33.00 










14.50 


20.80 


29.00 


32.50 


13.00 


-13.00 


0.00 


Jan. 30, I 


maximum 


21.20 


21. 10 


28.80 


32.80 










7.50 


15.60 


27.00 


32.30 


18.00 


-13.00 


2.00 



The minimum for Jan. 30 is certainly at the danger point for tree roots 
in bare ground, while under compacted snow it is 8.1°F. higher and under 
vegetation plus compacted snow it is almost 25° higher. The fruit 
grower cannot induce snowfall at his will but he sometimes has a choice 
between a slope where snow will remain and one where it will melt away 
with a little warm weather. He knows that knolls and wind swept spots 
in general are likely to need special care and that cover crops and wind- 
breaks tend to hold snow that might otherwise blow away. 

Different Systems of Soil Management. — A protective covering of 
vegetation can be provided by the grower with more surety than a snow 
covering. Table 43, arranged from data by Bouyoucos, 23 shows the 
effect of this covering on minimum soil temperatures at 3 inches depth. 
The superior protection afforded by cultivated, bare soil as contrasted 
with compacted soil is worthy of note. 

Table 43. — Average Minimum Soil Temperatures in Uncultivated and Culti- 
vated Soil and in Sod 23 
(Degrees Fahrenheit) 



Month 



Uncultivated 
(bare) 



Cultivated 
(bare) 



Sod 



Dec, 1914 
Jan., 1915 
Feb., 1915 



31.92 
31.11 
30.70 



33.26 
32.59 
32.49 



35.34 
34.55 
33.52 



Craig 51 in Iowa reported soil temperature at 6 inches depth on a 
January day, after hard freezing, two degrees warmer in sod than in 
cultivated soil. 

Depth of freezing is a fairly good indicator, though indirect, of soil 
temperature. Gourley 78 records observations made in New Hampshire 



WINTER INJURY TO THE ROOTS 307 

in March when freezing was at its greatest depth for the season; these 
are shown in Table 44. These figures are of special interest since they 
show the protective effect of increased cover-crop growth induced by 
fertilizer applications. The "cultivated with cover crop" plot had a 
scanty growth. 

Table 44. — Depth of Freezing as Affected by Soil Covering 

Clean cultivated (no cover crop) 16 inches 

Cultivated, with cover crop 15 inches 

Sod 12 inches 

Fertilizer, cultivation and cover crop 10 inches 

Fertilizer (excess nitrogen) cultivation and cover crop ... 7 inches 

Sandsten 165 made measurements of the depth of frost penetration in 
early February under different crops in Wisconsin. Table 45 shows his 

Table 45. — Frost Penetration under Different Cover Crops 166 

Bluegrass sod 18.0 inches 

Clean cultivation (no cover crop) 16.0 inches 

Rape 15.0 inches 

Oats 8.0 inches 

Hairy vetch 7.5 inches 

data. He interprets these observations to emphasize the protective 
value of an uncompacted cover, the bluegrass sod offering little insulation 
because of the lack of dead air spaces. He also considers the lower 
amount of moisture in sod land to have an important bearing. In 
connection with the data here cited from Gourley and from Sandsten it 
should be recalled that the soil does not freeze until its temperature is 
several degrees below 32°F. 

Oskamp 142 reports soil temperatures observed in Indiana with differ- 
ent soil covers. Table 46 is arranged from his data. It should be noted 



Table 46. — Monthly Minimum Soil Temperatures 142 
(Degrees Fahrenheit) 



Clean cultivation 
and cover crop 



Straw mulch 



Jan., 1915. 
Feb., 1915 
Dec, 1915 
Jan., 1916 
Feb., 1916 
Dec, 1916 




34.0 
34.0 
38.0 
35.0 
35.0 
35.0 



that this comparison is between straw mulch and land growing a cover 
crop, which has been shown to have higher minimum temperatures than 



308 



FUNDAMENTALS OF FRUIT PRODUCTION 



uncultivated or cultivated bare land or sod. A direct comparison of the 
extremes is not available, but by comparing minimum temperatures in 
bare land with those in sod (Tables 43 and 44), then sod with cover crop 
(Tables 44 and 45) and finally cover crop with straw mulch, some idea of 
the superior protective qualities of the straw mulch can be formed. As 
will appear later, the difference between safe and killing temperatures for 
roots is slight and a few degrees are apparently more important below 
ground than above. 

Soil Type. — Increased injury in sandy soil has been reported so 
frequently that the precise temperature conditions existing in the lighter 
soils should be examined carefully. Table 47 shows absolute minimum 
temperatures for certain months, recorded at a depth of six inches, in 
soils of different types. 



Table 47. — Absolute Minimum Temperatures in Different Soils 
(After Bouyoucos 23 ) 

(Degrees Fahrenheit) 





Gravel 


Sand 


Loam 


Clay 


Peat 


Dec, 1912.... 

Jan., 1913 

Feb., 1913 

Dec, 1914 

Jan., 1915 


29.0 
30.8 
21.1 
30.0 
30.5 
32.1 

28.9 


29.7 
29.1 
17.3 
25.3 
27.1 
32.4 

26.8 


30.3 
30.9 
22 3 
31.5 
31.4 
31.3 

29.6 


30.2 
31.2 
23.1 
30.3 
32.0 
31.9 

29.8 


31.4 
31.1 
19.1 
32.6 
32.4 


Feb., 1915 


32.2 




29.8 







These figures show a sufficient difference to indicate a possible cause 
for increased root killing in sandy soils. It should be stated, however, 
that Bouyoucos records a very marked tendency for all soils to assume 
a uniform temperature if air temperatures remain stable long. The 
lower minima in sand are due probably to more rapid conductivity so 
that a cold spell of short duration, as most cold waves are, would take 
effect here but be over before it would affect some of the other soils to 
the same extent. Thus, Bouyoucos states, "The 12-inch depth of 
gravel and sand froze Feb. 3, that of loam, clay and peat on Feb. 5, or 
2 days later; while the 18-inch depth of the various soils froze as follows: 
gravel, Feb. 6, sand, Feb. 8, clay, Feb. 10, loam, Feb. 11, that of peat did not 
completely freeze, its temperature remaining a few tenths of a degree 
above 32°F. throughout the rest of the winter." As to the effect of 
organic matter in soil, he comments on his investigations as follows: 
"The minimum temperature attained was highest in peat, slightly less 
and about the same in the various soils treated with peat and lowest in 



WINTER INJURY TO THE ROOTS 



309 



the untreated sand." A continued turning under in the spring of cover 
crops tends to raise the soil content of organic matter. The cover crop 
protects, then, while above ground by blanketing the soil and when 
turned under it affords some protection in the following winter through 
the increased amount of organic matter it has supplied. 

Soil Moisture. — -Another factor, possibly of equal importance, affect- 
ing root-killing in sandy soils, is the amount of moisture present. No 
evidence need be introduced here as to the comparatively low moisture 
content of the average sandy soil. Emerson 58 made" some very interest- 
ing studies of the effects of moisture on killing, in which lots of 25 
young trees each were exposed to a Nebraska winter, in boxes of loam 
soil with varying degrees of moisture. His tabular statement of results 
is reproduced here as Table 48. 



Table 48. — Root-killing of Apple Seedlings as 


Related to Soil Moisture 








Percent- 


Number of roots 


Box 


Where kept 


Soil cover 


age of soil 
















moisture 


Uninjured 


Injured 


Dead 


1 


Outdoors 


None 


10.4 





5 


20 


2 


Outdoors 


None 


15.2 





6 


10 


3 


Outdoors 


None 


19.8 


12 


10 


3 


4 


Outdoors 


None 


25.6 


13 


4 


8 


5 


Outdoors 


Straw mulch 


16.0 


18 


7 





6 


Outdoors 


Snow occasionally 


15.8 


10 


8 


7 


7 


Cool, dry cave 


None 


10.0 


25 









Emerson comments on his results in part as follows: "That the great injury 
to the seedling roots in the drier soils is not due directly to the dryness alone but 
to dryness and cold combined, is evident from the fact that the roots were 
absolutely unhurt in equally dry soil kept in a cool dry cave. . . . That dry- 
ness alone was not responsible is shown by the comparatively slight injury to 
roots in rather dry soil which was protected by a 4-inch mulch of straw, while 
roots in bare soil of almost the same moisture content were very badly hurt. 

"Just why severe freezing should injure roots worse in rather dry than in 
moist soil is not shown by the test reported above. On further investigation it 
may be found that roots are simply unable to withstand severe freezing or to 
recover from it unless surrounded by an abundance of moisture. Be this as it 
may, it is. quite probable that one cause of the great injury in rather dry soil is 
alternate freezing and thawing . . . the more water a soil contains the less 
subject it is to frequent alternate freezing and thawing. 

"The fact that the apple seedlings were much less seriously injured where 
protected by a mulch of straw than they were in bare ground is to be explained 
by the effect of mulches on freezing and thawing of the ground. The latter was 
tested during the winter of 1901-1902. The mulch protected the soil not only 



310 



FUNDAMENTALS OF FRUIT PRODUCTION 



against severe freezing during cold nights, but also against alternate freezing 
and thawing. The temperature changes observed on February 2, 3 and 4, 
1902 — a very cold period — are especially interesting. The surface of the bare 
ground thawed during the middle of the day and froze severely each night. Two 
inches lower, however, the soil did not thaw out during this very cold weather, 
though the temperature changes between day and night were great. The 
temperature of the mulched ground, both at the surface and 2 inches beneath 
it, remained constantly below the freezing point and, moreover, varied but little 
during the period." 

Recent studies by Bouyoucos 24 suggest an interesting possibility in 
this connection. He shows that in practically all agricultural soils some 

of the moisture remains unfrozen at ordi- 
nary temperatures and, indeed, even at 

— 78°C. The amount of unfrozen water 
varies with the kind of soil, becoming in 
general greater as the soils vary from the 
simple and non-colloidal to the complex 
and colloidal. The amount freezing at 

— 78°C. is very little, if any, greater than 
that freezing at — 4°C. It seems possible, 
then, that the increased amount of root 
injury in sandy soils may be due, in ad- 
dition to the lower amount of moisture in 
such soils, as mentioned above, to the ex- 
tremely small amount of water remaining 
unfrozen at temperatures only slightly 
below 0°C. while the finer soils have a 
reserve of capillary adsorbed unfrozen 
water under such circumstances. 

It should also be recognized that temperatures in the different soils 
may have been different. In any case, however, the result is the same; 
damage is greater in soils that are dry at the time of freezing. 

Relation of Cover Crops to Root Killing. — The effects of single factors 
on soil temperatures, and therefore on root killing, have been set forth. 
The value of a snow cover has been shown; the increase of soil tempera- 
tures with transition from bare ground through sod to cover crops has 
been reviewed; minima varying with the character of the soil have been 
indicated and finally dryness of soil has been shown to be associated 
with root killing. In orchard practice, however, these factors are rarely 
operative singly and some rather complicated interactions may be 
expected. 

Emerson's 59 studies on depth of freezing under two sets of conditions 
are of great importance since they show the interactions referred to above. 
Figures 30 and 31, reproduced from his studies, indicate depth of freezing 




Fig. 30. — Depth of freezing 
under various covers, in absence 
of snow. (After Emerson 59 ) 



WINTER INJURY TO THE ROOTS 



311 



without snow covering and with snow covering respectively. Under both 
sets of conditions the clean cultivated land froze deepest. More striking, 
however, is the different position occupied by the corn plot under different 
conditions. The reason becomes apparent, however, when the depth of 
snow covering on the several plots is considered. The close relation 
between depth of snow and depth of freezing, shown in all plots, is of 
interest. 




Fig. 31. — Relation of cover crops to depth of snow and depth of frozen soil. 

Emerso?i so ) 



(After 



Emerson's observations furnish more information: "Early in the 
winter ... it was noted that soy beans had very few leaves left and 
that the plants stood perfectly erect, furnishing almost no protection to 
the soil and that cowpeas, tho they still held their leaves, stood too 
erect to furnish much protection. The field peas, on the other hand, had 
held their leaves well and matted down nicely, forming a very good mulch. 
Corn was also found to have remained very erect as was also the case with 
cane and millet. Later in winter it was noted that the snow was held 
very well by corn, cane, millet, soy beans and cowpeas, while field peas 
and rye, the good covers, laid too flat on the ground to catch the 
drifting snow. The almost bare stems of such plants as soy beans, which 
still stood erect, held the snow much better than a plant like field peas 



312 FUNDAMENTALS OF FRUIT PRODUCTION 

which retained its leaves but matted down too close upon the ground. 
The stalks left standing after a crop of corn grown in the ordinary way has 
been harvested make a very efficient snow holder but furnish very little 
protection to the ground at times of intense cold unaccompanied by 
snow." 

The superior snow-retaining qualities mentioned, particularly in the 
case of corn, are operative mainly when the snow fall is accompanied by 
wind. 

Summarizing the requirements for a cover crop under Nebraska 
winter conditions, Emerson says: "It should start growth promptly in 
order to insure an even stand and to choke out weeds. It should grow 
vigorously to insure a heavy winter cover and to dry the ground in case 
of late-growing trees so as to hasten their maturity. It should be killed 
by the early frosts so that it will stop drying the ground after danger of 
late tree growth is passed and help to conserve our light rains so much 
needed by the trees in winter. ... A cover crop should be heavy 
enough to furnish as good direct protection as possible against freezing 
and thawing and it should stand sufficiently erect to hold snow against 
the power of strong winds." 

Of the crops tried, that which appeared to come nearest meeting these 
requirements in Nebraska was German millet. 

Root Killing in Different Fruits. — There is less latitude in the root 
hardiness of the various species than in the hardiness of their tops. 
Nevertheless there are enough differences in many cases to make the 
choice of root stocks very important. 

The Apple. — Carrick 35 found that the majority of dormant apple roots 
were seriously injured at a temperature of — 12°C, with considerable 
injury at — 7°C. He reports the cambium as the most tender tissue, 
followed closely by the phloem, with the cortex less tender. Under 
extreme conditions xylem and pith are said to be killed. French-grown 
stocks were found substantially as hardy as the native-grown seedlings. 
In all cases there was a considerable variation, as would be expected 
among seedling plants. This difference, it may be remarked, is likely 
to assume considerable importance under field conditions. 

The Pear. — Studies on pear roots by the same investigator indicated 
that Kieffer roots were more resistant than the French stock. A tem- 
perature of — 11°C. during the dormant period produced extensive injury 
in both. In April Kieffer showed only slight injury at — 9°C. while 2-year 
French roots were killed. Pear roots seemed to acquire hardiness later 
than those of the apple and never become quite so hardy. 

The Peach. — The peach root is relatively hardier in the zone of dis- 
tribution of this species than is the apple root along the northern border 
of apple growing. Occasionally, however, root killing in peaches occurs. 
Goff 76 records that in the freeze of 1899 peach tops suffered more than the 



WINTER INJURY TO THE ROOTS 313 

roots; Green and Ballou 81 indicate peach root killing in Ohio. Macoun 115 
reports similar injury to thousands of peach trees in southern Ontario 
in the winter of 1898-1899. However, root killing without any appreci- 
able amount of injury to the top, as occurs from time to time in the apple, 
is extremely rare in the peach; conditions severe enough to injure peach 
roots generally will work far greater damage to the tops. 

Carrick 35 summarizes the results of laboratory freezing of peach roots as 
follows: "As a general rule the order of resistance of the various tissues in the 
peach root seems to be as follows: pith, cortex, phloem, cambium, xylem. At 
— 18°C. or below, the xylem was usually killed during the hardiest period. In 
most cases during February and March the pith is the tissue most easily killed, 
but in April the cambium is the least resistant. 

"It is not so easy, with the data at hand, to assign an arbitrary limit within 
which the peach root is injured by freezing. This is because of the great varia- 
tion in the root tissues. The peach cambium certainly is as hardy as the pear 
cambium, tho less so than the apple. Regardless of the size of the root, most 
of the peach material tested showed some injury at — 10°C, and, except in 
unusual cases, serious injury occurred at —11°. This would then place the 
hardiness of the peach root very close to that of either pear seedling." 

The Cherry. — Sour cherries frequently suffer from root killing on the. 
northern margin of their range, sometimes under conditions such that the 
top is uninjured. Hansen 85 states: "One great difficulty in cherry grow- 
ing in this state is the tender imported Mahaleb and Mazzard stocks upon 
which we are compelled to bud and graft at present. These root-kill in 
severe winters." Under some conditions the flower buds of sour cherry 
may be more resistant than the roots. Craig 50 reported on damage to 
cherry stocks in Iowa in 1898-1.899: "In nursery, the former [Mazzard] 
was practically a total loss of 2-year-olds and a complete loss of 1-year-old 
in the region of the severe root killing. Mahaleb suffered less. Morello 
stock and own-rooted Morello trees generally escaped with slight injury, 
except in exposed situations. ... In the college nurseries the practice 
of root grafting the cherry received commendation by the fact that the 
only trees which escaped were those which were partly on their own roots." 
Prunus pennsylvanica is reported from several sources to be hardy but is 
difficult to work commercially. 

Carrick 35 places the relative hardiness in cherry stocks in descending 
order as follows: Mahaleb, Prunus Besseyi, Prunus pennsylvanica, 
Mazzard and he finds the Mahaleb generally much hardier than the apple 
roots investigated. "In large Mahaleb roots during their hardiest 
period," he states, "little injury is found under — 14°C, while at — 15° the 
injury is relatively small. . . . The Mazzard roots in no instance with- 
stood — 11°, but the number of tests run at — 10° was insufficient to place 
this as its minimum. From these results the Mazzard cherry stock does 
not appear hardier than Keiffer pear stock." 



314 FUNDAMENTALS OF FRUIT PRODUCTION 

The Plum. — Iowa's experience with plums in the winter 1898-1899 is 
thus stated by Craig: 51 "Plums, native or European, worked on peach 
or Myrobolan killed, on Marianna badly injured, on Americana slightly 
injured, but these recovered rapidly except where they were, in a few 
instances, permanently injured. . . . Americanas worked on peach roots 
escaped where well rooted from the cion. Sand cherry stock (PrunusBes- 
seyi) has been used to some extent in the state. In no case have I found 
these roots injured in the slightest degree. In passing I may add that ex- 
perience has not yet developed the ultimate effect of this stock upon the cion. 
Thus far its dwarfing influence upon varieties of the Americana type is 
satisfactorily demonstrated. Domestica plums on own roots fared better 
than the same varieties on peach, Myrobolan or Marianna." Elsewhere: 
"On the matter of plums the sand cherry (Primus Besseyi) appears to be 
the hardiest form we know anything about. Native plums in the college 
orchard on this stock were entirely uninjured last winter, while the same 
varieties on Americana stocks alongside were injured or killed." Carrick 
places Myrobolan in the same group as Mazzard cherry and pear for 
hardiness. 

The Grape. — Reports of root killing in grapes are relatively rare. The 
comparatively deep-rooting habit, combined with sufficient tenderness of 
tops to discourage grape growing in regions where root killing is common, 
may account for this apparent resistance. Furthermore, most grapes 
of American origin are in fact hardy varieties on their own roots and if it 
be safe to reason from the analogy of cion-rooted trees, the roots should 
share the hardiness of the tops. Niagara has been reported to be notor- 
iously tender in bud and root. 73 Hansen 85 reports considerable trouble in 
parts of South Dakota from root killing ; the New York vineyards suffered 
extensive damage in the winter of 1903-1904. Hedrick 92 suggests that 
the St. George (a variety of rupestris) stock used in some experimental 
work at Geneva, N. Y., may be more hardy than certain others and notes 
that American varieties on their own roots winter killed extensively. 

Carrick made numerous laboratory freezings of six varieties of grapes to 
compare their relative hardiness. The varieties studied, representing several 
species, fell readily into two classes, viz., Clinton, Concord and Diamond, "rather 
resistant to cold" and Cynthiana, Lindley and Norton, "relatively easy to kill 
by freezing." Within the groups the differences in hardiness are not striking. 
For the hardier group, "Only scattering injury is recorded at —11°, —12°, and 
— 13°C. At an exposure of —14.5°, 22 out of 27 Concord roots were uninjured, 
and only a trace of cambium and cortex injury was noted in the remainder. 
... At —18°, however, the cambium, phloem, and cortex tissues were com- 
pletely injured in all roots, with some xylem injury in the Diamond and the 
Concord. . . . The limits of this second group (Cynthiana, Lindley and 
Norton) he between —10° and — 12°C, the roots usually undergoing con- 
siderable injury at —11°. In relative hardiness this places these varieties 



WINTER INJURY TO THE ROOTS 315 

between the Mazzard cherry and the apple. The Clinton, Concord, and Dia- 
mond roots, even excluding the influence of size, are considerably more resistant 
than apple roots, and Concord and Clinton seem equal if not superior to the 
Mahaleb stock. 

" . . . Vitis aestivalis, represented by Norton and Cynthiana, is not adapted 
to severe cold, and this may account for the fact that its range is limited to the 
South. The tenderness of Lindley is probably due in part to the influence of 
Vitis vinijera, which, as is well known, will not survive the winter in the latitude 
of New York State without much protection. Concord and Diamond represent 
Vitis labrusca, the Northern Fox grape, which, while restricted in distribution, is 
found in Maine. Vitis vulpina, represented by Clinton — a variety with extremely 
resistant roots — has the greatest range of any American species of grape, it 
having been found in Canada north of Quebec." 35 

The Small Fruits. — Among small fruits Carrick found a wide range 
in hardiness. The blackberry, dewberry and red raspberry roots tested 
appeared to rank with the Myrobolan plum and the Mazzard cherry. 
Eldorado seemed the hardiest of the blackberries under observation, but, 
curiously enough the Lucretia dewberry seemed somewhat more hardy 
than Eldorado. The roots of the Cuthbert raspberry appeared equal in 
hardiness to the Eldorado blackberry. None of the varieties studied 
survived a temperature of — 12°C, though many of the larger roots were 
uninjured at — 11°C. On the other hand, currant and gooseberry roots 
were extremely resistant; a Downing gooseberry root withstanding 
— 20.5°C, though this probably would be the limit of hardiness. On the 
basis of the material examined Carrick rather provisionally rates the 
gooseberry roots as slightly more resistant than the currant. 

Preventive and Remedial Treatments. — Danger of root injury may be 
permanent or temporary. If the past history of the locality shows 
extensive root injury the grower should bear this in mind as a possible 
threat. If his site is sandy or chronically dry or wind swept in winter he 
is threatened continually and may be justified in accommodating his 
orchard practice accordingly. A temporary condition of danger may 
occur, such as a dry autumn, in orchards ordinarily safe. Early winter 
cold snaps are most to be feared, because the roots are then tender and 
there is less likely to be a snow covering. However, it may be February 
that brings disaster. 

Deep Planting and Mulching. — Preventive methods are more effi- 
cacious and generally cheaper than palliative measures. Deeper planting 
than usual, if the winter water table is not too high, may protect the 
roots, especially in the first winter. Protective soil coverings, either 
mulches or cover crops, should be used in very dry locations; the advan- 
tage of a snow blanket should be remembered in choice of site or in select- 
ing a cover crop. 

The tendency of deep planted trees to send out roots from the cion is 
well known. Some varieties do this more freely than others. These 



316 FUNDAMENTALS OF FRUIT PRODUCTION 

roots when they come from cions of extremely hardy varieties are gen- 
erally hardier than the stocks commonly used. In those of the northern 
sections where root killing is most likely there is a tendency to grow trees 
formed by grafting long cions on short pieces of root for the purpose of 
inducing cion rooting, thus securing increased hardiness in the roots. 
No experimental evidence is available to show clearly whether cion roots 
of hardy apple varieties are hardier than those of tender varieties, but 
Craig 51 records numerous instances when cion roots proved more hardy 
than the stocks on which they were worked. Hansen, 86 writing in South 
Dakota, says: " . . .in ordinary winters the roots emitted by the 
scions of hardy varieties are sufficiently hardy but . . . they are not 
proof against such winters as that of 1898-1899." 

Use of Hardy Stocks. — Top working on stocks of known hardiness is 
another method of combating root killing in those sections particularly 
subject to it. Pyrus baccata is said by Hansen to succeed in the Trans- 
baikal section of Siberia where the mean annual temperature is 27°F. 
and the mean temperature of the coldest month — 18.4°F. and where 
the annual rainfall is 11.42 inches. He reports young seedlings of this 
species to have wintered perfectly despite a temperature of — 40°F. with 
no snow. The "Virginia crab" is also reported to be more hardy than 
French crab. However, these have more or less dwarfing effect and do 
not make an altogether satisfactory union. 119 

Pruning. — After the damage has occurred, there is little that can be 
done. If the killing is complete or nearly so the trees should be removed. 
However, many times the root destruction is incomplete; some of the 
roots that start straight down from the crown on old trees will frequently 
escape. In many of these cases a heavy pruning back, or, if there is 
also injury in the top, a moderate pruning back, will enable the tree to 
survive and still have many years of usefulness. Very young trees 
that have suffered only partial destruction of the roots can be restored 
in many instances by banking the trunks with earth, inducing the for- 
mation of additional cion roots. 

Handling Nursery Stock in Cold Weather. — One form of root injury 
likely to be encountered in regions remote from the territory commonly 
subject to killing of this type is that occurring on nursery trees. Root 
growth in apple trees in Missouri has been shown to continue long after 
the top has assumed a completely dormant appearance, in fact until 
winter has well set in. 212 In a growing state, it will be recalled, roots 
are damaged by temperatures only a few degrees below freezing and 
even in a dormant state they will stand only comparatively high tem- 
peratures. 38 Chandler states: "In case of 1-year-old roots of the French 
crab, used as stock by most of the nurserymen, about —5 to — 8°C. (23 to 
15.8°F.) is as low a temperature as they can be depended upon to with- 
stand with no injury." Fall dug trees, necessarily lifted before the 



WINTER INJURY TO THE ROOTS 317 

ground freezes and often dug rather early must have very tender roots, 
so tender in fact that exposure to a slight frost after digging in this stage 
is likely to have very serious consequences. Extreme care in protecting 
tree roots against any freezing from the time they are dug until they 
are planted is amply justified. 

Summary. — Root killing is particularly common in sections with 
low winter temperatures and little snowfall. Minimum soil temperatures 
of 24° to 25°F. at a depth of 6 inches are very common in deciduous fruit 
sections and soil temperatures of 7°F. have been recorded in Nebraska. 
Freezing temperatures are frequently registered to a depth of 2, and occa- 
sionally to a depth of 3 feet. The critical temperature for the roots 
of most hardy species during their dormant season ranges from about 
14° to 5°F. During the growing season it is much higher. Minimum 
soil temperature is influenced greatly by soil covering, being distinctly 
higher under, snow or a mulch formed by some cover crop than under 
bare ground. Fertilizers may indirectly protect roots against severe 
freezing by promoting the growth of weeds or of cover crops. Frost 
penetrates more deeply in light than in heavy soils. Roots are killed 
more readily in dry than in moist soils. Considerable differences exist 
in the relative resistance of the roots of different species and varieties. 
Preventive measures include moderately deep planting, the use of cion- 
rooted trees or trees on hardy stocks, the choice of locations not unduly 
exposed to the wind, the use of cover crops to hold the snow and thus 
both directly and indirectly blanket the soil and in some cases artificial 
mulching. Remedial treatment consists chiefly in judicious pruning. 
Care should be taken in handling nursery stock that the roots are not 
exposed to freezing temperatures in packing, unpacking or heeling in 
and they should be protected from freezing while in storage or transit. 






CHAPTER XVIII 
WINTER INJURY IN RELATION TO SPECIFIC FRUITS 

The discussion of winter killing to this point has been general. Any 
species furnishing convenient illustrative material has been drawn on 
and most of the types considered affect each species more or less; the 
prevailing conception has been the tree in general rather than any specific 
kind. There are, however, differences in the problem of hardiness as 
it relates to the several species and detailed points of adjustment to 
these differences. These can be considered more conveniently by dis- 
cussing each fruit singly, evaluating for each the different types of injury 
to which it is liable and indicating, wherever possible, the best means 
of minimizing the difficulties. 

The Apple. — The apple is the most widely grown fruit in America 
and is, at one point or another, exposed to practically every form which 
winter injury can take; it seems, however, practically immune to some 
of them. Aside from sunscald there is little or no evidence that the 
apple suffers from those types of injury that are characteristic of late 
winter, i.e., from warm weather followed by cold. Though killing of 
fruit buds sometimes occurs it seems hardly probable that this is a kill- 
ing of buds which have broken the rest period. At the time of the 
Easter freeze of 1920 in the lower Missouri valley many varieties had 
pushed their buds so far along that they showed pink. These varieties 
of course suffered more or less but their killing constitutes a case of 
damage to succulent tissues rather than of winter injury. Late blossom- 
ing varieties, though the buds had swelled noticeably, were not damaged 
by the drop to 14°F. Though this is not conclusive evidence it is sugges- 
tive. A February freeze of — 7°F. in Georgia when some Japanese plums 
were in bloom, worked serious injury to plums and peaches but caused 
no damage to the apple. 157 

Whipple 209 introduces clear evidence of fruit bud killing in Montana 
and shows that little readily recognized evidence that the buds have been 
fruit buds is left after they are killed. If the injury is confined to the 
floral parts as Whipple has shown to be the case at times, the vegetative 
parts grow and the casual observer concludes that the tree has failed to 
form fruit buds and is going through an off year. It is, therefore, 
possible that this killing may occur at times when it is not recognized. 
Nevertheless it is safe to assume that fruit bud killing is comparatively 
rare and that when it does occur it is not necessarily related to the 
breaking of the rest period. 

318 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 



319 



Injuries Associated with Immaturity. — Difficulties due to prolongation 
of the growing season are far more common in the apple. Indeed, disre- 
garding the winter drought conditions in the north prairie states, which 
are not apple growing states in a commercial sense, it is, in one form or 
another, the prevailing type of injury. A large proportion of recorded 
cases of winter injury may be traced to immaturity. This probably 
accounts for the many cases observed in which the wood is killed while 
the buds are not. The various forms of injury associated with imma- 
turity have been discussed and require no elaboration here. 

There remain for consideration, however, some interesting differences 
between varieties in hardiness. Most European varieties were early 
found lacking in this respect along the Atlantic coast and the apples 
developed in the eastern states in turn proved tender when transplanted 
to the northern prairie states. From available data it is not yet possible 
to reduce varietal differences from an indefinite empirical status to a 
basis capable of quantitative expression. Macoun's statement, quoted 
above under Immaturity, that hardiness is merely an expression of 
complete maturity, is undoubtedly true in a large measure. The winter 
apples of southern latitudes are tender at the north though there are 
exceptions, as Ben Davis which is probably hardier than Baldwin, and 
the winter apples of the north, hardy there, are summer or fall apples in 
the south. The summer apple in the north, finishing its active season 
early, has time to develop maturity such that it withstands the winters ; 
the winter apple must grow longer to complete its cycle and has less oppor- 
tunity to acquire the condition that makes it hardy. As an index of 
comparative maturity Beach and Allen 16 report observations on the date 
of terminal bud formation in several varieties, which are reproduced here, 
with some change of arrangement, as Table 49. Despite some incon- 



Table 49. — Date of Forming Terminal Buds 16 



Variety 



Nursery 
trees 



Orchard 
trees 



Variety 



Nursery 
trees 



Orchard 
trees 



Hibernal 

Oldenburg. . . . 

Salome 

Soulard 

Virginia 

Wealthy 

Mcintosh 

Silken Leaf . . 

Winesap 

Anrsim 

Black Annette 



July 25 


July 1 


Aug. 20 


July 1 


Aug. 20 


* 


Aug. 20 


* 


Aug. 20 


* 


Aug. 20 


July 12 


Aug. 28 


* 


Sept. 1 


* 


Sept. 5 


Julv 22 


Sept. 5 


* 


Sept. 20 


* 



Ben Davis . . . 

Gano 

Jonathan .... 

Patten 

Grimes 

Delicious. . . . 

Ingram 

Iowa Blush . . 
Lansingburg . 

Minkler 

Roman Stem 



Sept. 27 
Sept. 27 
Sept. 27 



July 1 
July 10 
July 22 
July 1 
July 15 
July 22 



Terminals not formed at time of first frost, about Oct. 1. 



320 



FUNDAMENTALS OF FRUIT PRODUCTION 



sistencies, as, for example, the relative positions of Winesap, Ben Davis 
and Delicious, there is a general correspondence between the date of ter- 
minal bud formation and the generally accepted relative hardiness of the 
varieties reported upon. 

The water content of most tissues may be taken as an index of matur- 
ity, diminishing as this condition is approached; the same is true of other 
tissues. This being true a study of the moisture contents of different 
varieties ought to give an index of their relative maturity. 

Shutt 180 reports an interesting set of moisture determinations at Ottawa, 
reproduced here as Table 50. These 10 varieties were arranged by Macoun in 
groups in decreasing order of hardiness, as follows: Group 1 (hardiest), Olden- 
burg, Yellow Transparent, McMahon White; Group II, Wealthy, Scott's Winter; 
Group III, Scarlet Pippin, Walworth Pippin; Group IV (least hardy), Hebble 
White, Boy's Delight, Blenheim Pippin. 

Table 50. — Percentage of Water in Apple Twigs Jan. 23, 1903 180 



Variety 



Basal portion 



Terminal 
portion 



Whole twig 



Yellow Transparent 
McMahon White. . . 

Oldenburg 

Walworth Pippin . . . 

Boy's Delight 

Wealthy 

Scarlet Pippin 

Hebble White 

Scott's Winter 

Blenheim Pippin . . . 



45 . 55 
45.45 
45.02 
44.72 
44.74 
46.82 
47.13 
49.09 
47.50 
48.93 



45.10 
46.96 
47.51 

47.67 
44.75 
48.72 
49.92 
48.82 
50.36 
51.38 



45.30 
46.14 
46.15 
46.20 
46.25 
47.70 
48.58 
48.91 
48.98 
50 . 24 



Comparison of Macoun's arrangement with Shutt's figures, considering 
in particular the terminal portions of the twigs, shows a correspondence 
that at least suggests a relationship. Shutt comments on these figures in 
part as follows: . . . "it would seem, therefore, that we have direct 
and definite proof that there is a distinct relationship between the mois- 
ture content of the twig and its power to resist the action of frost and 
that those trees whose new growth contains the largest percentage of 
water, as winter approaches, are in all probability the most tender." 

Table 13 shows the moisture content, at different dates, of several 
varieties of apples. Of these Hibernal and Wealthy are generally 
recognized as the hardiest. It is significant that these two varieties 
had the least moisture in July and that in January, after a week of cold 
weather, including a minimum of — 15°F., having lost the smallest 
amounts of moisture, they had the greatest moisture contents. Winesap, 
figures for which were not complete, dropped in water content, between 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 321 

July 15 and Dec. 26, from 60.4 to 45.7 per cent., having on that date the 
lowest water content. It is also the least hardy of the varieties under 
consideration. The hardier varieties were found to lose less water 
through the bark in a given time. 

Various workers have studied the structure of apple twigs but no one 
has been able to correlate definitely any structural differences with hardi- 
ness or its lack. There seems some tendency for hardier varieties to 
have somewhat thicker bark and more starch in their tissues but these 
characters are by no means constant. Were the starch content shown to 
be correlated, it could hardly be regarded as a causal agent but more 
likely a product of the conditions that make the variety hardy, through 
making it mature. 

In short, then, the only character that can be linked definitely with 
hardiness in the apple is maturity. If one variety is hardier than another 
because it matures better, the cultural practices that make the tender 
variety mature better make it in effect more hardy. A well matured 
tree of a tender variety is undoubtedly more hardy than an immature 
tree of a hardy variety. This accounts for many apparent inconsistencies 
in field observations. 

Control Measures. — Efforts have been made to influence cold resist- 
ance by topworking upon stocks of great hardiness. In so far as root 
killing is prevented this practice has proved beneficial. It is also a wise 
practice if the growing of varieties notoriously subject to crown rot or 
crotch injury is to be undertaken. However, that hardiness of stock 
increases the hardiness of the cion is not shown conclusively by any 
evidence available. It is conceivable that an early maturing stock might 
influence the top slightly in the same direction but any influence of this 
character is comparatively insignificant. Macoun 119 reports top grafting 
varieties not perfectly hardy on stocks of very hardy varieties at Ottawa, 
Ontario; among the cions used were Baldwin, Benoni, Esopus, Falla water, 
King, Newtown, Northern Spy, Ontario, Rhode Island, Rome Beauty, 
Sutton, Wagener, Winesap and York Imperial; the stocks used were 
McMahon, Gideon, Haas and Hibernal. The grafts endured several 
winters, but "the test winter of 1903-1904 killed practically all of them," 
though the stocks survived. It is, however, interesting to note that 
Sorauer 183 considered that grafting of weak growing varieties upon 
vigorous stocks results in an increased amount of frost canker, character- 
istic of immature tissues. 

There is a limit to the effects that can be induced by cultivation. 
No amount of cultural manipulations can make a variety mature its 
fruit and its wood in a situation where it does not receive sufficient heat 
(where the season is too short). It is not without significance that only 
one of the important winter apples of the south can be grown to any 
advantage in the north. Whether the cause be called failure to mature 

21 



322 FUNDAMENTALS OF FRUIT PRODUCTION 

or lack of constitutional hardiness, there is a northern limit to the culture 
of every variety and that limit is reached more quickly for some varieties 
than for others. 

Varietal Differences. — Out of the vast and costly experiments in hardi- 
ness carried on by planting and replanting, the sieve of selection has shown 
certain varieties to withstand winter cold in average conditions better than 
others. Since Baldwin is perhaps the best known single variety in most 
sections where apple hardiness is important it is used as a standard of 
reference. Hardier than Baldwin is a quality possessed by but few varie- 
ties of extensive commercial possibilities though this statement does not 
mean that Baldwin is particularly hardy. In the list of varieties recom- 
mended by Hedrick, Booth and Taylor 88 for the St. Lawrence and 
Champlain Valleys, where Baldwin does not succeed, are Fameuse, 
Mcintosh, Oldenburg, Wealthy, BluePearmain, Jewett Red, St. Lawrence, 
Gravenstein, Red Astrachan, Yellow Transparent, Canada Baldwin, 
Longfield and numerous crab apples. 

For "the most northerly district" of Quebec, Macoun 119 recommends 
Tetofski, Blushed Calville, Lowland Raspberry, Duchess, Charlamoff, 
Antonovka, Wealthy, Hibernal, McMahon, Longfield, Patten Greening, 
Mcintosh, Milwaukee, Winter Rose, Stone, Scott Winter and Malinda. 
It is stated that the summer and autumn varieties are the hardiest. 

At the Northwest Experiment Farm, in Minnesota, where winter con- 
ditions are probably as severe as at any point where apples can be 
expected to grow, the list of approved varieties is limited, aside from 
certain crab apples, to four: Hibernal, Oldenburg, Okabena and Patten 
Greening. 178 

If one variety were to be picked as the hardiest of all cultivated 
varieties of the apple grown in America it would probably be Hibernal. 

The Pear. — The pear is like the apple in its reactions to winter con- 
ditions. It is somewhat less hardy than the apple. Though apples are 
grown at points where the mean temperature of December, January and 
February is 13°F., the northern limit of the pear follows in general the 
mean temperature line of 20°F. 66 Nevertheless certain varieties possess 
considerable hardiness. Though evidence as to actual hardiness in the 
northern Mississippi valley is not available because of the complications 
introduced by fire blight prevalence, some information may be secured 
from experience in certain eastern states where blight is not so serious. 

Pears suffered extensive injuries in New York during the extremely 
severe winter of 1903-1904. 64 Young trees, though the bark and wood 
were discolored, made good recovery, in one case forming a layer of 5 
millimeters over the old sap wood in the first summer. Trees that had 
been injured by psylla were killed outright in many cases. Dehorning 
old trees that were injured aggravated their poor condition. 

Waite 198 reports extensive damage to pears in the Hudson River 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 323 

valley during the same winter. Pointing out that pear orchards are 
planted customarily in low rich ground, in other words, on sites more 
inviting to winter injury than those ordinarily chosen for peaches, he 
states that pears were as severely injured as peaches and do not possess the 
recuperative powers of the peach. Elevation made great difference in 
the amount of damage. "The young pear trees are rather less hurt than 
the older trees, as in the case of the peach, but it should be noted in this 
connection that young pear trees having the wood blackened, although 
they will push out their wood and make a start, are very apt to decline or 
else maintain their life in a very feeble manner as a result of the dead 
wood at the heart. They have not the ability to recover by depositing a 
thrifty layer of sap-wood. Pear trees under 3 or 4 years of age which are 
badly frozen and which show blackened or discolored wood, even though 
the bark may look normal from the outside and may appear to be alive 
and quite fresh when cut into, should be cut off below the snow line 
and allowed to sprout." 

Injury to pears occurred in the localized Michigan freeze of October, 
1906. 193 Though peaches were killed, it was only in low places and in 
vigorously growing trees that pears were seriously injured. Blackening 
of the wood was found. Apples were very little injured under the same 
conditions. In parts of Washington an early winter freeze caused split- 
ting of trunks on the south side and blackening in the wood of the fruit spurs 
down to the limbs, with damage in some sections to the blossom buds. 12 
Bailey 8 reports killing of fruit buds at Ithaca, N. Y., with no injury to 
wood, during a dry cold winter. Injury to wood occurred elsewhere, he 
states, at the same time, but evidently he does not consider this severe. 

The following varieties have been reported suitable for culture in 
Vermont and hence presumably hardy : Vermont Beauty, Flemish Beauty, 
Anjou, Winter Nelis, Onondaga, Tyson, Lawrence and Sheldon. 205 As 
"succeeding in many gardens" Angouleme, Bartlett, Buffum, Seckel, 
Louise Bonne de Jersey are mentioned. At Orono, Maine, a little beyond 
the northern limit of the Baldwin apple, the hardier varieties have been 
found to be Clapp Favorite, Flemish Beauty, Howell, Lawrence, Sheldon 
and Winter Nelis. 139 Chandler states that Anjou is one of the hardiest 
varieties at Ithaca, N. Y., probably a little more so than Clapp Favorite 
and Sheldon, certainly less than Flemish Beauty. Bartlett is generally 
conceded to be rather tender. 

Flemish Beauty has proved the hardiest variety of the better class of 
pears tested at Ottawa, Ont. 114 Evidence elsewhere corroborates this 
selection, though even this variety is by no means immune to winter 
injury in regions of commercial fruit growing. 17 

The Peach. — The difference in the hardiness problem in peaches 
north and south has been discussed, maturity being stated as the leading 
factor in the north, the rest period in the south. Root killing has been 



324 FUNDAMENTALS OF FRUIT PRODUCTION 

shown to be of relatively small importance in the peach, though it is by 
no means unknown. Extensive killing occurred in the Michigan peach sec- 
tion in a freeze on Oct. 10, 1906, while the trees were still in full foliage. 193 
At South Haven the temperature fell to 17°F., and some unofficial ther- 
mometers registered 6°F. Cambium and sap-wood injuries extending to 
the snow line were common. Frost cankers on peach trunks and crotches 
are found sometimes, following winters of extreme cold or a late growing 
season. 98 "Gum pockets usually form under the flattened areas and the 
gum often oozes out during periods of wet weather. The injured area is 
usually rather indefinite about the margin and the formation of a healthy 
roll of callus is thereby much retarded." 

It has been shown earlier that no stated temperature can be assumed 
as fatal. However, fruit buds are generally more tender than wood. 
When, therefore, there occur cases in which the wood is killed and the 
buds survive, they may be considered good evidence of lack of maturity. 
There is hardly a winter without some killing back of young twigs which 
may be interpreted as indicating a lack of maturity. The care generally 
exercised in selecting sites for peach orchards to secure freedom from 
spring frosts fortunately has another equally desirable, though seldom 
recognized, effect in that it secures greater maturity. There is a remark- 
able uniformity, throughout reports of various freezes in northern 
states, in locating the greatest injury in trees growing in moist, rich soil 
and receiving late cultivation. Another point of agreement is the ascrib- 
ing of great injury to trees low in vitality from various causes such as 
San Jose scale, leaf curl, low fertility, borers and poor drainage. Green 
and Ballou 81 mention an orchard in which the San Jose scale spray was 
omitted in 1902 on three rows running through the middle. In the 
severe winter of 1903-1904 these three rows were killed while the rest 
were uninjured. Whether the greater injury to weak trees is actual and 
due to some specific condition characteristic of weakness or whether it is 
apparent and due to their inferior recuperative powers is not clear. A 
given degree of injury would be more evident, certainly, on a weak than 
on a strong tree. 

Waite, 198 reporting on the January, 1904, freeze in New York, dis- 
tinguished three classes of injury: " (1) In bearing peaches the trees most 
injured by freezing show the bark entirely blackened and dead, more or 
less separated from the trunk and the wood turned a very dark brown 
color. The injury extends far up onto the limbs although the bark 
usually has not separated on the branches. Such trees are dead beyond 
all question. The bark on such trees still retained its vitality. Some- 
times a rise of 10 or 15 feet resulted in trees being less seriously 
injured. (2) With many peach trees the bark is lightly separated from 
the wood which is of a dark-walnut color next to the cambium and brown 
throughout. Though still alive the bark is somewhat browned and 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 325 

discolored, the youngest or outer la} r er of wood has been frozen until it is 
now of a dark-walnut color and the wood is blackened throughout. 
Many of these trees are of doubtful vitality and will probably succumb. 
Others have enough vitality to enable them to pull through. Where 
bark is adhering or only partially separated from the trunk the chances 
for recovery are good. The tops of such trees are usually found in fair 
condition, the wood brownish, but the white cambium layer uninjured 
though lying immediately in contact with brown, dead wood. The 
twigs, especially the 1-year wood, sometimes have been frozen so badly 
that they will not be able to push out the leaf buds. In severe cases the 
leaf buds themselves are killed, but, as a rule, they are still alive. Of 
course on all such trees the fruit buds are killed. The most injured part 
is the trunk just above the snow line. ... (3) The third class, which 
may be described as the moderately frozen trees, in which the wood above 
the snow line is blackened but the bark not separated from the wood and 
with the cambium still apparently alive, although water-soaked and 
injured, frequently has minute brown streaks in the bark immediately 
in contact with the cambium. Such trees will almost invariably 
recover. . . . Nearly every tree in the entire Michigan fruit belt 
was frozen in February, 1899, so that the wood was blackened and dead 
clear to the bark. A new layer of live white wood formed inward from 
the white bark, the trees made a fairly good growth, having no fruit crop 
to carry, and bore the year following a record fruit crop." 

As in the apple, the bark on the trunk near the ground seems to 
mature late and is particularly liable to injury. After seasons favoring 
late growth mounding of earth to cover this region somewhat has been 
found very profitable insurance. In several instances in Ohio in 1903- 
1904 a few shovelfuls of earth at the crown made the difference between 
dead trees and uninjured trees. 81 

Chandler 39 records an interesting case of mild injury associated with 
immaturity. After a very rainy August in 1914 the minimum for 
the winter, — 9°F., occurred late in December. In the following spring 
the blossoms of several varieties were at least three weeks late in opening. 
Examination disclosed injury to the pith of the bud, extending even as far 
as the pith of the twig. There was very little injury elsewhere. Usually 
the flower parts are less resistant than the pith of the bud and of the 
twig. The temperature evidently was not low enough to kill matured 
buds but it did damage the immature tissues. The trees in question bore 
a normal crop that season. Similar cases have been observed at other 
times. 14 

Treatment of damaged trees consists of the ordinary prophylactic 
measures and a moderate pruning. Very heavy heading back, or 
dehorning, has proved decidedly injurious when the bark or the wood is 
damaged; a fair amount of pruning is, however, beneficial. 83 This 



326 FUNDAMENTALS OF FRUIT PRODUCTION 

should be done before growth starts. There is a general tendency to 
overestimate damage and immediately after a freeze many orchards 
have been taken out which would have recovered in time had they been 
allowed to remain. Trees with any considerable injury to the trunk 
should by no means be allowed to bear fruit in the season following the 
injury. 76 

Observations by Mer 132 on oaks may explain the injurious effects 
of very heavy pruning. Investigating old winter injuries of the "black 
heart" type, he found considerable starch still in the injured wood but 
little in the wood subsequently laid down, indicating that the tree was 
unable to withdraw starch from the injured tissue. This suggests that 
if the injury is extensive the tree will have difficulty the following spring 
in securing sufficient carbohydrates to sustain growth until a supply can 
be secured from the new leaves. If the pruning is heavy enough to 
remove all the buds which make new growth most readily the difficulty 
must be increased. If, however, no buds are removed the scanty carbo- 
hydrate supply is apportioned to so many growing points that none 
receives enough to sustain growth until it can become self-supporting and 
the tree dies of carbohydrate starvation. 

Hardiness in wood and in bud are not always combined in the same 
variety. Elberta, generally considered hardy in wood, seems tender in 
the fruit buds. Hedrick, 89 reporting a questionnaire of New York and 
Michigan peach growers, states their selections for wood hardiness as 
follows: For New York in order named, Crosby, Hill's Chili, Stevens' 
Rareripe, Gold Drop and Elberta; for Michigan, Hill's Chili, Crosby, 
Gold Drop, Kalamazoo and Barnard. Jaques Rareripe, Wager, Carman, 
Belle of Georgia, Hale's Early, Champion and Greensboro are listed as 
hardier than the average in this respect. Early Crawford, Late Craw- 
ford, Chair's Choice, St. John and Niagara are rated as the five most 
tender in wood of the varieties commonly grown in New York. Salway 
is listed as tender in Michigan. 

In fruit buds, New York growers find greater hardiness in Crosby, 
Hill's Chili, Triumph, Gold Drop, Stevens' Rareripe and Kalamazoo; 
Michigan growers find Hill's Chili, Gold Drop, Crosby, Kalamazoo and 
Barnard hardiest. Concerning the five most tender varieties in bud 
there is entire agreement in New York and Michigan as to the order of 
their tenderness: Early Crawford, Late Crawford, Chair's Choice, 
Reeves' Favorite and Elberta. The Peento group is extremely tender. 

The Cherry. — Sweet cherries are generally known to be far more tender 
than the Dukes, Amarelles and Morellos. As outlined by Finch 66 the 
northern range of cherries is marked by the mean winter temperature of 
about 16°F. For the three coldest of the pomological districts into 
which the United States is divided in the fruit catalog of the American 
Pomological Society only one variety of sweet cherry, Black Tartarian 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 327 

is recommended and that recommendation is confined to one district. 
For the same districts 13 varieties of Duke and Morello cherries are 
recommended. 158 Of 26 varieties in the catalog, 13 are recommended 
for District 1 and of these, 10 evidently are considered worth growing in 
District 2 which includes most of the northeastern fruit growing sections. 
The three leading commercial varieties, Early Richmond, Montmorency 
and English Morello, are considerably hardier than the Baldwin apple. 
However, some of the hardiest apples appear to be hardier than the hard- 
iest cherries. Hansen 85 states that root killing is the one great difficulty 
in cherry growing in South Dakota. Following the February, 1899, freeze, 
with a minimum of -27.5°F., at Madison, Wis., some root killing was rep- 
orted, but most varieties brought their fruit buds through, Large Morello, 
Late Morello, Shadow Amarelle, Dyehouse and Ostheim having over 
90 per cent, live buds. 76 Curiously enough many varieties undamaged 
in the 1899 freeze had their buds killed in the winter of 1896-1897 with a 
minimum of — 23°F. During the summer of 1896 the trees had been in 
sod and there was much dry weather. Considerable variation in the 
hardiness of the embryo flowers, not alone between varieties, but on the 
same tree and even within the same bud, has been reported. 75 Careful 
study showed a strong inclination toward tenderness in varieties having 
the greater number of flowers per bud and a similar susceptibility in 
individual buds within the variety. The periphery of the tree had 39.9 
per cent, live buds while the central part had 69.9 per cent, alive. GofT 
did not regard this difference as due alone to the greater number of flowers 
in the peripheral buds but suggested that it might be due to the protection 
afforded by the branches and to conduction of heat along the trunk from 
the soil. Roberts, 161 also working in Wisconsin, reported that though 
winter injury to cherry buds is frequent in that state, it is rarely severe 
enough to affect seriously the yield of fruit. Frequently only one or two 
of the four or five blossoms within the bud are killed. Studies made in 
the spring of 1917 are interesting in several respects. All injury had been 
confined to blossom buds. Older trees showed more injury than young 
and the exposure appeared to have little relation to the amount of injury 
during that winter. Trees which had been partly defoliated by the shot 
hole fungus the previous season received less bud injury than normal trees. 
The shortest and the longest spurs were less injured than spurs of medium 
length and on terminal shoots there was less injury in the buds at the 
base and at the tip than along the central portion of the shoot. Larger 
buds were most frequently injured. 

The injury occurred early in December following a temperature of 
-12°F. and could not have been due to development excited by warm 
winter weather. Microscopic study showed that the buds most 
damaged were the most advanced in their development. Late maturity 
could not have been the factor involved as the trees and parts of trees 



328 FUNDAMENTALS OF FRUIT PRODUCTION 

growing latest were the least injured. This finding is in agreement with 
Goff's earlier report of greater tenderness in the winter of 1896-1897 when 
the trees stood in sod and the weather was dry, both of which conditions 
favor early formation and rapid development of fruit buds. It appears, 
then, that cultural practices tending to promote vigorous growth and 
fairly late maturity would have some effect in reducing injury of this sort, 
though Roberts states that it could not be eliminated altogether. 

In a general way, it may be said that the cherry is not very liable to 
injuries associated with immaturity. Some varieties of sweet cherries 
were slightly injured in Michigan in October, 1906, when peach trees were 
killed and pears considerably injured in some places. 193 Cherries, how- 
ever, showed considerable injury in Washington in late November, 
1896, at a temperature somewhat below 0°F. 12 

Bessarabian, Brusseler Braun, Lutovka, English Morello and Early 
Richmond appear, from the scant data available, to be the hardiest of 
the commonly grown varieties. 

The Plum. — Perhaps because of the number of botanical species from 
which the cultivated varieties have sprung, plums show a wide range in 
hardiness; though some are more tender than the majority of peaches, 
others are hardier than the hardiest apples. Hedrick 91 states that the 
Nigra plums are the hardiest of our tree fruits and are able to resist 
nearly as much cold as any cultivated plant. Only a little less hardy are 
the Americanas. The relative hardiness of the other groups is thus 
summarized by Hedrick: "Insititias as represented by Damsons come 
next with varieties of Domestica as Arctic, Lombard and Voronesh 
nearly as hardy. The Domesticas are less hardy than the apple, ranking 
in this respect with the pear. Of Domesticas the Reine Claude plums 
are as tender to cold as any though some consider Bradshaw more tender. 
. . . The Triflora (Japanese) plums vary more in hardiness than any 
other of the cultivated species. Speaking very generally they are less 
hardy than Domesticas, the hardiest sorts, Burbank and Abundance, being 
somewhat hardier than the peach, while the tenderest varieties, of which 
Kelsey is probably the most tender, are distinctly less hardy than the 
peach. Of the remaining plums, the Hortulana, Munsoniana and 
Watsoni groups, there are great diversities in opinion as to hardiness. 
Probably all the varieties in these last groups are as hardy as the peach 
with a few sorts in each more hardy than the peach. It is to be expected 
from the more northern range of the wild prototypes that the Hortulana 
and Watsoni plums are somewhat hardier than Prunus Munsoniana.'" 

Waugh 204 indicates distinct varietal ranges, within the species: 
" The tenderness of Bradshaw seems to belong more to the fruit buds than 
to the wood and correspondents do not seem to agree in their reports; 
but upon the basis of statistics received, we may trace the northern limit 
of the Bradshaw . . . which runs from 100 to 300 miles south of the 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 329 

line traced for Lombard. ... In fact a majority of the standard varie- 
ties, such as Coe Golden Drop, Italian Prune, Jefferson, Lincoln, Moore 
Arctic, Pond, Shippers' Pride and Washington, would probably be found 
to conform fairly well to the same limits as Lombard." Of the Japanese 
plums, "Abundance, Chabot (Chase, Yellow Japan), Hale, Red June, 
Willard and Ogon seem to be about as hardy as Burbank. Satsuma 
stands about midway between Burbank and Kelsey." 

In North Dakota, Waldron 209 states: "Only one species of plum 
(Americana) can be grown with any success in the State. So far as 
tried here they are all hardy though some ripen late and most of them 
are vigorous and productive. ... All things considered they are the 
easiest and most profitable fruit to grow in North Dakota. . . . For 
general cultivation the following varieties will be likely to succeed: De 
Soto, Forest Garden, Weaver, Cheney, Wolf, Rolling Stone, and Wyatt." 
In parts of Minnesota Rolling Stone, De Soto, and Surprise are too late in 
ripening their fruit to be satisfactory in cultivation, though they are not 
stated to lack hardiness. 41 For the colder parts of Vermont several 
varieties have been reported to be as hardy as the sugar maple : Stoddard, 
Hawkeye, Quaker, Aitkin, Surprise, Cheney, De Soto, Forest Garden, 
Wolf, Wyant and Weaver. 205 

In Wisconsin many varieties have brought their buds through a tem- 
perature of — 38°F. in one winter, though they succumbed to — 23° in 
another, 76 indicating that the condition of the tree makes a considerable 
difference in the amount of cold that can be endured. In view of the work 
of Chandler with peaches and Roberts with cherries it seems possible that 
the advancement of the buds when they enter the resting stage may 
have much to do with their hardiness. No definite data are available, 
unfortunately, on this point, but the superior hardiness of the Americana 
group, which is late in maturing, appears to justify investigation. It 
would seem, since plum blossoms are injured more frequently than the 
woody parts, that maturity might be delayed safely to some extent 
without unduly increasing liability to injury in other ways. 189 

Recent investigations in Minnesota indicate that some of the injury to plum 
blossoms is associated with early breaking of the rest period. Treatment to 
increase hardiness by retarding blossom formation and development would tend 
also to delay the breaking of the rest period. 

The Grape. — Winter killing is not so prominent a factor in grape 
growing as it is with some of the tree fruits. Two reasons may be assigned 
for this comparative freedom from injury. First, varieties grown com- 
mercially in the majority of sections subject to winter killing are de- 
scended, at least in part, from the native species and therefore profit 
from the adjustment of the native species to their environments* Second, 
the difficulty of securing satisfactory ripening of the fruit, because of 



330 FUNDAMENTALS OF FRUIT PRODUCTION 

the shorter growing season, tends to limit the northward spread of grape 
culture to points with winter extremes well within the adaptation of 
the vine. 

Nevertheless, the grape is far from immune to winter injury. Varie- 
ties with Vinifera qualities predominating or from species native to 
regions of mild winters have distinct climatic limitations and even 
the so-called hardy varieties frequently suffer. There is little evidence 
to connect winter drought with winter injury except in so far as a dry 
soil freezes deeper. Heavy winter irrigation has proved of no value 
with Viniferas in New Mexico. 72 Under very severe conditions root 
killing may occur; at times the vines are killed to the ground and there 
are frequent instances of killing of fruit buds because of imperfect matu- 
rity. Gladwin 73 records three seasons out of eight at Fredonia, N. Y., 
when the vines did not reach proper maturity. Sometimes heavy rains 
late in the growing season bring about this condition; again it may 
be due to the ripening of a heavy crop. The light crop usually following 
a heavy fruiting is commonly ascribed to exhaustion of the vines but 
it may be due also, at least in part, to the killing of a large number of 
imperfectly matured buds. Since the grape bud is compound and mixed, 
the primary floral parts may be killed and only the secondary shoot 
develop the following spring. This tends to obscure the killing and the 
sterility of the shoot is attributed to exhaustion following the heavy 
crop of the preceding season. Gladwin shows that the three lightest 
crops of the period studied followed the seasons when the sugar content 
of the grapes (an index of maturity) was lowest. However, since vines 
which have not borne are affected also much of the immaturity must 
come from other causes. Indeed, Budd 27 considered immaturity and 
tenderness to result from the lack of a crop and remarked that the wood 
of Rogers' hybrids ripened well when bearing a crop but without a crop 
did not mature. Much greater injury has been reported in low ground, 
particularly in ground with poor drainage. 

At times very low temperatures, even when the vines are mature, 
will cause a discoloration of the wood without actually killing the vine. 

Anthony 4 reports recent investigations of the practicability of 
growing certain Vinifera varieties in the eastern United States. When 
a moderate amount of winter protection is given, by bending the vines 
down and covering with a few inches of earth, very satisfactory results 
are obtained. Indeed, with the varieties tested, the limiting factor 
seemed to be the heat and length of the growing season rather than tender- 
ness to winter cold. Anthony states: "A well matured Vinifera is seldom 
killed outright by the winter even if given no protection, but the effect of 
the first winter is usually to decrease the plant's vitality to such an 
extent that it is unable to reach proper maturity the next season and so 
is usually killed the second winter. " 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 331 

Mounding has been effective in protecting Vinifera grapes in New 
Mexico 72 and hardy grapes in Iowa were satisfactorily wintered by a 
slight mounding about the trunks and a slight covering of the tips of 
the canes with soil. 27 Straw protection has been less satisfactory on 
Viniferas in New York than laying the vines down and giving a slight 
earth covering. Vines treated in this last manner have proved hardy 
in very trying climates. 

Severe freezes in grape growing regions damage all varieties so that 
a close estimate of hardiness in such places is difficult. However, as 
the culture extends into colder regions varietal differences become more 
evident. The American Pomological Society's catalog highly commends: 
for Section I, Brighton, Cottage, Diamond, Herbert, Lady, Lindley, 
Moore Early, Moyer, Niagara (?), Victor, Winchell (Green Mountain), 
Woodbury and Worden; for Section II, Janesville and Winchell; for 
Section XIV, Diamond is the only variety to receive even a qualified 
recommendation. 158 

For Vermont, Waugh 202 recommends Moore Early, Worden, Moyer, 
Brighton, Wyoming Red and Green Mountain. The Northwest Minne- 
sota Experiment Station for a more trying situation recommends Beta, 
Janesville and Campbell Early. 178 Hansen in South Dakota expresses 
preference for Worden, Concord and Moore Early in favorable situations 
and for unfavorable locations, Janesville. 85 The difficulty with Concord 
in Vermont appears to arise, not from its lack of hardiness but rather 
from the brevity of the growing season. 

THE SMALL FRUITS 

Though winter killing in cane fruits is common, more common, 
perhaps, than it is among tree fruits, conditions of plant and environ- 
ment favoring or reducing injury are far less understood. This is due, 
in part to the large number of units involved so that the loss of a few 
plants is hardly noticed, in part to the short normal life of a cane fruit 
plantation so that even an extensive loss is not as calamitous as that of 
an orchard and in part to the quick recovery of the plants from the com- 
mon forms of winter injury. When a tree trunk is severely injured 
recovery is a matter of several years, if indeed it is ever complete. 
Raspberry or blackberry canes, on the other hand, may kill to the ground 
but only one crop is lost and the following autumn generally finds the 
plants in as good condition as ever. 

The growing of small fruits has, in most of the northern sections, 
because of these conditions, developed along two lines; in some cases only 
hardy varieties are grown and no winter protection is given and in others 
protection is given and desirable varieties grown regardless of their 
hardiness. Hence inquiry into hardiness as it relates to small fruits 
generally has taken the form of variety testing for this quality; related 



332 



FUNDAMENTALS OF FRUIT PRODUCTION 



experimental data are very meager. Field observations as recorded are 
frequently contradictory and puzzling. A certain variety, for example, 
half hardy in New York would be expected to be wholly adapted to 
Georgia; actually it may prove fully as tender in the south as in the north. 
The red raspberry as a group is generally conceded in northern regions to 
be hardier than the blackcap group yet the reverse condition obtains over 
wide areas. 33 Though loganberry and other western dewberries are very 
tender, in one winter at Corvallis, Ore., with a minimum of 20°F., when 
Cuthbert raspberries were killed at the collar the loganberry was un- 
harmed. Furthermore, cane fruits frequently suffer from drought injury 
which is doubtless sometimes confused with winter injury and so reported. 

Winter injury to cane fruits may take one of several forms. Root kill- 
ing occasionally occurs, especially in dry, cold climates with little snow. 
Where this occurs, covering the canes is of no avail unless the roots 
also are covered. In other cases the canes may kill to the ground, or 
they may kill part way back, or the laterals may kill. Immature canes 
appear to kill more easily at the tips and close to the ground and would 
sometimes be benefited by mounding. The canes may be weakened only 
and blossom but fail to mature the crop. Under exceptional conditions 
currant and gooseberry fruit buds may be killed while the stems live. 

Immaturity Most Important. — It is a generally accepted principle in 
the growing of cane fruits that maturity is important to hardiness. Imma- 
ture tips, laterals on canes pinched back and suckers that develop late are 
sometimes injured by comparatively mild freezing; a temperature of 12°F. 
in November has caused extensive damage to raspberry tissues of this 
sort in Missouri. Even in Virginia caution about late cultivation, 
inducing an immature and tender growth, appears necessary. 3 That the 
degree of maturity attained at the onset of cold weather can be modified 
by cultivation, irrigation and fertilization is obvious. 

Relation of Summer Pinching to Maturity. — The effect of pinching 
on raspberries in northern sections where maturity is clearly a factor 
with tree fruits is well illustrated by Table 51, which shows the resistance 
to winter killing of different varieties pinched at 15 to 20 inches and of the 
same varieties unpruned. It is evident that the lateral growth induced 
by pinching is not so hardy as the unbranched canes; presumably this is 
due to immaturity. 

A statement of Michigan experience is not without interest. 195 
"Hansell, King, Miller [red raspberries] seldom branch and should not 
be pinched back. When allowed to grow naturally the canes form strong 
buds from which the fruiting branches will be developed the following 
season while if the ends are pinched the buds will develop the first year 
into slender shoots upon which the fruit buds will be weak, . . . [with 
an] increased tendency toward winter-killing. Hence, for non-branching 
varieties pinching back is not to be recommended." However, Card 33 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 



333 



Table 51. — Winter Resistance of Pruned and Unpruned Raspberries 49 

(10 = no injury) 



Heebner 

Springfield 

Royal Church 

Carman 

Thompson Early Prolific. . 

Herstine 

Parnell 

Golden Queen 

Reider 

Brandy wine 

Niagara 

Marlboro 

Hansell 

Clarke 

Cuthbert 

Turner 

Caroline 

Average 

Average pruned, 6 . 08 
Average unpruned, 7 . 29 



Pruned 



Protected Unprotected 



9.0 
9.0 
2.0 
7.0 
8.0 
7.0 
8.0 
5.0 
8.0 
8.0 
7.0 
7.0 
8.0 
7.0 
7.0 
9.0 
8.0 

7.3 



4.0 
7.0 
2.0 
5.0 



4.0 
6.0 
4.0 
4.0 
6.0 
5.0 
4.0 
6.0 
6.0 

4.9 



Unpruned 



Protected Unprotected 



10.0 
9.0 
4.0 
9.0 
9.0 
9.0 
8.0 
8.0 
8.0 
9.0 
9.0 
9.0 

10.0 
8.0 
9.0 
9.0 
9.0 

8.6 



5.0 
7.0 
5.0 
8.0 
7.0 
6.0 
5.0 
5.0 
4.0 
7.0 
6.0 
5.0 
7.0 
5.0 
7.0 
6.0 
7.0 

6.0 



reports instances in which canes growing fairly late in the season have 
been hardier because they were smaller and of more compact growth and 
in reality better matured. It is worthy of note, also, that it is a common 
practice among dewberry growers in the South Atlantic states, where 
winter injury to cane fruits is by no means unknown, to mow all canes 
after the fruit has been picked; evidently no serious winter killing to the 
late growing shoots results. 

Varietal Differences from Year to Year. — Phenological notes on 
cane fruits are not sufficiently extensive to indicate whether there is any 
correlation between varietal behavior in regard to maturity and resistance 
to cold weather. Comparison of the dates of ripening of fruit with the 
recorded degree of winter killing fails to establish any connection; the 
same is true with regard to the date of blossoming. There is, furthermore, 
some inconsistency in varietal behavior. Table 52, arranged from reports 
on variety tests of blackberry in Massachusetts, shows a considerable 
fluctuation in the percentage of canes killed in successive winters, with a 
considerable difference in varieties. Thus Agawam's record is 30-0-0 
while Erie's is 20-20-80. This indicates that more than one factor must 



334 FUNDAMENTALS OF FRUIT PRODUCTION 

be operative in determining hardiness and that though maturity is 
frequently very important, it is by no means to be considered the sole 
factor. 

Table 52. — Percentage of Blackberry Canes Killed in Successive Winters 125 

1890 1891 1892 

Agawam 30 

Early King 10 12 8 

Erie 20 20 80 

Minnewaski 8 5 

Snyder 10 

Wachusett 20 10 

Western Triumph 30 8 3 

Wilson 20 5 40 

Injuries from Drought not Uncommon. — Any variety may be weak- 
ened from drought or fungous diseases and suffer unduly the following 
winter. It is well known that large amounts of moisture in the soil 
induce winter killing and that accumulation of ice on the surface of 
the soil has the same effect. The relation of winter drought to winter 
killing is perhaps less appreciated. Some unpublished investigations 
by Emerson in Nebraska on this matter are of great importance, 
pointing as they do to the conclusion that " injury to raspberries 
in that locality was apparently almost wholly a matter of winter 
drying." 61 Canes coated with paraffin suffered no appreciable injury 
while untreated canes on the same stools were killed to the ground or to 
the snow line. Observing that when the snow cover was deep enough 
to keep the soil from freezing the canes were not injured, even in the 
parts that projected above the snow, Emerson tried to secure the same 
results by mulching. Various mulches were tried and the ground was 
in many cases kept from freezing but the canes were killed down to the 
mulch. "Temperature readings taken at various depths in the mulch 
indicated that for a period of some weeks a portion of the mulch was 
continuously below the freezing point. Of course, the water absorbed by 
the roots from the unfrozen ground could not pass through the frozen 
part of the cane. Other studies suggested, though I perhaps did not 
have sufficient data to prove it, that the canes are not frozen for any 
length of time when surrounded by snow." 61 

Card 33 remarks that though in Nebraska covering of raspberries 
and blackberries is necessary the same varieties are commonly grown in 
New York without protection, despite the fact that the winters in 
Nebraska are no colder. He reports that during one winter in Nebraska 
when the mercury fell below zero (Fahrenheit) but once, with —5° as the 
minimum, unprotected canes were killed. Plants in adjoining rows 
exactly alike, except that they were laid down and covered, were entirely 
uninjured. The following winter was much colder but the soil was moist 



WINTER INJURY IN RELATION TO SPECIFIC FRUITS 335 

from autumn rains and both raspberries and blackberries came through 
in good condition without protection. Growers of raspberries in Wyom- 
ing are advised to stop irrigation about Aug. 1 but to give a heavy late 
fall irrigation, besides covering the plants. 29 There is general agreement 
that cane fruits suffer more in seasons and in sections with little snow. 

It is possible that much of the benefit attendant upon covering canes 
comes from the reduced drying out rather than from actual protection 
from cold. Even a trivial protection seems sufficient, sometimes just 
enough to hold the canes down. Lying prostrate without covering they 
escape most of the drying effect of the wind; when covered with earth 
or snow they will resist extreme cold. Such protection is essential in 
some sections, in others the profit in the operation depends on the 
variety grown. Thus, in some experiments at Ottawa it was found that 
the increased yield resulting from protection of the hardiest varieties 
did not repay the cost of the operation though other less hardy varieties 
thus treated gave 16 to 22 per cent, greater yields or enough to leave a 
profit for the work. 48 Incidentally, it was reported that the plants thus 
protected ripened their crops 5 to 8 days ahead of those not protected. 
In Colorado minimum temperatures around zero ordinarily do not neces- 
sitate covering raspberry canes; 93 in New York unprotected raspberry 
plantations stand considerably lower temperatures without material 
injury. 

Group and Varietal Characteristics. — The small fruits as a class 
exhibit a rather wide range of hardiness. Currants probably are to be 
regarded as the hardiest of all cultivated fruits, with gooseberries only 
slightly less so. Next in order, in the north at least, come the red rasp- 
berries descended from native species — those of Europe are tender — 
followed by the blackcap raspberries which in turn are hardier than the 
blackberries. There is some overlapping; the hardier black raspberries 
are hardier than the more tender of the red raspberries and some black- 
berries in turn are hardier than certain of the raspberries. Least hardy 
of all are the dewberries, which are really tender though their trailing 
habit makes possible their culture much farther north than their upright 
hybrids with the blackberry can be grown without protection. The 
dewberry and the blackberry, like the plum, are derived from several 
native species and their range in hardiness is correspondingly wide. The 
loganberry, Phenomenal berry and allied forms are tender to tempera- 
tures below 15°F. and the Himalaya and Evergreen blackberries are 
very little, if any, hardier. On the one hand, then, is the currant, hardier 
without protection than the apple or the plum; on the other is the dew- 
berry, rather less hardy than the peach though it is sometimes grown 
where the peach is not grown, because it is more easily protected. 

Among currants the smaller Red Dutch and Raby Castle types are 
considerably hardier than the large-fruited varieties, the Fay and Cherry 



336 FUNDAMENTALS OF FRUIT PRODUCTION 

types. 121 Gooseberries rarely suffer from winter killing but where 
comparison has been possible Houghton seems the hardiest, with Down- 
ing and Industry only slightly less resistant. Turner seems for a long 
time to have been considered generally the hardiest of the older red 
raspberries; though the newer Sunbeam and Ohta appear even hardier, 
a large number of varieties, such as Hansell, Marlboro and Herbert, 
are hardy enough for all but the most trying climates. Hardier than 
many of the red raspberries, particularly those with European ancestry, 
are the hardiest blackcaps, including Plum Farmer and Older. Of the 
blackberries, Snyder is generally the hardiest, with Eldorado and Agawam 
ranking close to it. Lucretia is perhaps the most widely grown dewberry 
in the northern states, being grown successfully in Iowa and Minnesota 
when covered with soil through the winter. 

Summary. — Though winter injury from other causes sometimes 
occurs, both the apple and the pear suffer most from those forms asso- 
ciated with immaturity. Certain cultural practices encourage earlier 
maturity, but in these fruits protection against winter injury is most 
readily secured by a judicious selection of varieties. The peach, plum 
and cherry suffer from injuries associated with immaturity and with 
an early breaking of the rest period, the latter being the most important 
with the peach and certain plums and the former with other plum groups 
and the cherry. Protective measures lie principally in controlling season 
and degree of maturity, though something can be accomplished by selec- 
tion of varieties. Grapes suffer mainly from those forms of winter 
injury associated with immaturity. Varieties show great differences 
in their hardiness. In addition to the protective measures adapted to 
the tree fruits protection by artificial covering of the canes during the 
winter is sometimes practicable with this fruit. The small fruits show 
a wide range in hardiness, some of them, as the currant and gooseberry 
being among the hardiest and others, as the western dewberries, being 
very tender. The bramble fruits, in addition to being subject to a 
general killing back, are particularly susceptible to injury at the crown. 



CHAPTER XIX 

THE OCCURRENCE OF FROST 

Though spring and autumn frosts determine the geographic limits 
of certain fruits less frequently than minimum winter temperatures, 
they are nevertheless of no small importance in fruit production. There 
are some whole sections of the country, as for instance the high table 
lands of eastern Oregon, where fruit growing is very uncertain because 
frost may occur at almost any time during the growing season. There 
are many other sections or areas where spring frosts frequently occur 
so late that certain fruits such as the apricot or the almond cannot be 
successfully, or where autumn frosts are so early that late maturing 
fruits such as the grape do not ripen properly and consequently are not 
grown. Furthermore, within regions or sections that are suitable for 
fruit culture there are many sites or locations which, because of their 
susceptibility to frost, are unsuited for orchard purposes or where, if 
fruit is planted, it requires expensive artificial protection from frost. 
Finally, there come years when untimely frosts levy a heavy toll on 
the fruit crop in isolated places or over wide areas generally considered 
to be favorably located for fruit production. Early autumnal frosts 
seldom cause concern so far as the season's crop is concerned, though in 
grapes and some of the late maturing or everbearing types of small 
fruits they may be responsible for considerable damage. On the other 
hand, comparatively few and exceptionally fortunate are the fruit growers 
who are entirely free, year after year, from concern about possible spring 
frosts. The cost of full protection from spring frosts of certain pear 
orchards in the Rogue River valley has amounted sometimes to $40 
per acre. It is quite likely, however, that many crop failures arising from 
other causes are attributed to frost damage and it is certain that much 
can be done to lessen this injury by the careful selection of kinds and 
varieties of fruit adapted to the particular situation or by selecting 
a situation suitable to the kinds or varieties of fruit that it is desired to 
grow. Furthermore, under favorable circumstances much can be accom- 
plished by palliative methods, such as heating the orchard. 

FROST FORMATION 

Though discussion of the nature, occurrence and prediction of frosts 

belongs properly in treatises on meteorology, a brief outline of the 

more important facts concerning frost formation, so far as they concern 

the fruit grower, seems necessary here because this subject is not studied 
22 337 



338 FUNDAMENTALS OF FRUIT PRODUCTION 

so widely as is warranted. It should be understood, however, 
that cold weather aside from frosts may damage fruit crops and it is 
not always necessary that the temperatures go below the freezing point. 
Dorsey shows that cold weather, though the temperature remains above 
freezing, immediately following the pollination of certain plum varieties, 
results in such a slow growth of the pollen tube that abscission of the 
style often takes place before fertilization, the result being as complete 
failure to set fruit as though frost had actually occurred during the 
blossoming period. Low temperatures also prevent the bees from 
effecting pollination. 

Frosts and Freezes Distinguished. — Furthermore, not all freezing 
temperatures are clue to frosts. English writers use the term "frost" 
to designate freezing temperature of any kind but usage in the United 
States restricts "frost" to a kind of cooling well recognized and limited 
in its scope. A "freeze," as distinguished from a frost, is due to the 
importation of cold air from other regions and may be accompanied by 
a high wind; a frost is due to a local cooling of air and occurs during 
calm weather. A frost may take the form called a "hoar" frost, with 
a visible deposit of frozen moisture, or it may be a "dry " or " black frost " 
with freezing temperatures but with no deposit. Freezing temperatures 
may accompany snow squalls. All of these may injure orchard fruits. 
Against freezes the fruit grower is generally unable to contend by 
palliative methods; against frost much effort has been expended and it 
is upon frost that much horticultural thought has been centered. 

Relation of Radiation to Frost. — Some knowledge of the nature of radiation 
is necessary to a proper understanding of the nature of frost. It is generally 
considered by physicists that all substances are constantly receiving and emanat- 
ing heat. This radiation heat travels in straight lines through ether and through 
air, being absorbed by them little or none. Striking a solid substance it is in 
part reflected and in part absorbed, the amounts of reflection and of absorption 
varying with the substance. During a clear day the heat received by any sub- 
stance through radiation from the sun and from other substances is in excess of 
the amount emitted through radiation; during a clear night the heat lost by 
radiation exceeds that gained. On a cloudy day the sunlight is cut off to a 
great extent and the substance is warmed less than on a clear day; during a 
cloudy night much of the heat lost by radiation is reflected by the clouds and the 
substance is cooled less than on a clear night. There is some absorption of 
radiant heat by the atmosphere. Radiant heat from the earth is absorbed by 
water vapor, carbon dioxide and ozone. 

Radiation is proportional to the exposed surface, and the amount of heat 
stored and available for radiation is to a large extent proportional to the volume 
of the radiating substance. Therefore vegetation, which has a large surface in 
proportion to its volume, cools by radiation with relative rapidity. 

Though air freely permits the passage of radiation heat, it radiates little 
itself in comparison with other substances. There is, it is true, an appreciable 



THE OCCURRENCE OF FROST 339 

amount of radiation from the air. The rapid cooling of air after sunset is largely 
a radiation effect, especially if the air at higher elevations is rather free from 
water vapor as is usually the case with a high barometer. However, in compari- 
son with radiation from the earth's surface that from the air is small. Coming 
in contact with radiating and therefore cooler substances, air loses heat to them 
by conduction and is thereby cooled. If the air is in motion, the cooled air and 
the warmer air form a mixture which is constantly coming in contact with the 
radiating substances bringing to them fresh supplies of heat. If, on the other 
hand, the air is calm, the cooling of the radiating substances and therefore of the 
adjacent air continues as long as conditions remain stable, frequently till the 
sun rises. 

Temperature Inversion. — Evidently the nocturnal cooling of the 
air is largely dependent on the cooling of the earth's surface by radia- 
tion. The cooling effect is, therefore, most marked near the surface, 
but since on even the stillest night the air becomes somewhat mixed its 
temperature may be affected for from 200 to 600 feet above the surface, 
the effect becoming less with increasing height. 136 During the day the 
temperature decreases at the normal adiabatic rate with increasing 
distance from the earth. This relation is unchanged at night except in 
so far as it is disturbed, as shown above, by radiation up to a height of 
200 to 600 feet. There is, then, at night, first an increase in temperature 
with distance above the earth, followed by the normal adiabatic decrease. 
This phenomenon is known to meteorologists as the temperature inversion. 

The extent of the temperature inversion is indicated by Table 53, showing the 
averages of observations made throughout the year at varying heights above a 
thermometer placed on grass and fully exposed to the sky, expressed in relation 
to the readings of this thermometer. The steepness of the inversion varies from 
night to night and it is more marked in some localities than in others but it 

Table 53. — Average Temperatures at Different Heights Compared to that 

in Grass 111 

Distance above Grass Increase (Degrees Fahrenheit) 

1 inch 3 

6 inches 6 

1 foot 7 

12 feet 8 

50 feet 10 

150 feet 12 

necessarily exists whenever frost occurs. This temperature inversion causes 
frost but it also makes possible the combatting of frosts by orchard heating as 
shown later. Humphreys 97 points out another interesting relation of this in- 
version to frost damage :" . . . it is obvious that the tops of open and sparsely 
foliaged trees, especially if rather tall, often are less subject to frost and more 
easily protected than are the lower limbs. On the other hand, when the tree is 
low and its outer foliage sufficiently dense to produce a protecting canopy over 
the under and inner branches, as is generally the case with orchard trees, the 



340 FUNDAMENTALS OF FRUIT PRODUCTION 

difference between the free radiation from the exposed fruit and the restricted 
radiation from that which is covered may usually be sufficient, even when there 
is a marked temperature inversion, to subject the former and not the latter to the 
greatest danger from frost and freeze." 

Radiation and Thermometer Readings. — The full importance of radia- 
tion to the horticulturist needs emphasis. Lack of recognition of this 
factor has diminished the value of much investigational work. A ther- 
mometer exposed to the open air is radiating and receiving heat. During 
a clear night the outgoing exceeds the incoming heat and the thermometer 
registers a lower temperature than that of the air. Inside a shelter prac- 
tically all the outgoing radiation heat is reflected to the thermometer 
which consequently registers very close to the actual air temperature. 
During May in cranberry marshes in Wisconsin there were found differ- 
ences between sheltered and exposed thermometers over bare soil averaging 
2.3°F. for all nights of record, including nights not clear. Occasionally 
the exposed thermometers recorded as much as 5.7 and 6.4° lower than 
the thermometers in shelters. 46 Inasmuch as these temperatures were 
taken near the ground it is possible that they represented extreme con- 
ditions and would be of direct importance only to the cranberry and 
strawberry grower. Sheltered and unsheltered thermometers at a 
height of 5.5 feet from the ground at Williamstown, Mass., showed dif- 
ferences at the time of the minimum temperature averaging 1.6° and 
a maximum difference of 4°F. 134 It is evident, then, that the exposed and 
sheltered thermometers do not check and that the differences are not 
constant. 

Radiation and Plant Temperatures. — Plants as well as thermometers 
lose heat by radiation. Seeley 176 working with strawberries found con- 
siderable difference between plant temperatures and air temperatures. 

He reports in part on his results as follows: "The plant thermometer readings 
were usually lower than the air temperature in the early morning, the minimum 
usually being about 3 or 4°[F]. lower than the air, the difference being greater, 
of course, when the weather was clear with but little wind velocity. The plant 
cooled off more rapidly than the air in the early evening so that at 7 p. m. it was 
usually 3 or 4°[F.] lower in temperature than the surrounding air." At times 
the temperature of the plant may fall to 8°C. below that of the surrounding air 
and plants may be frozen stiff though the thermometer indicates one or two 
degrees above zero (C.), 151 and there are records showing that occasionally plants 
are cooled by radiation to a temperature 12 to 15°F. below that of the surrounding 
air. 112 Tomato vines under apple trees sometimes escape frost when those 
exposed to radiation are killed and the temperature on a lawn under a tree may 
be 5° higher than in the open. 138 

Observations, predictions and conclusions, then, must be made with 
three standards in mind: the air temperature, the exposed thermometer 
temperature and the plant temperature. Though the exposed ther- 



THE OCCURRENCE OF FROST 341 

mometer doubtless registers closer to the plant temperature than the 
sheltered thermometer, it must be remembered that predictions 
are based on and apply to sheltered thermometer readings. The dif- 
ferences between the three temperatures may not be great but they are at 
times great enough to vitiate conclusions drawn from observations and 
they may conceivably become at times great enough to have material 
effects. 

Dewpoint and Its Relation to Frost. — Air is commonly known to 
contain more or less water vapor. Other things equal, the higher its 
temperature the more vapor it can contain and conversely the lower its 
temperature the less moisture it can hold. If, therefore, any sample of air 
be cooled enough it will reach the point where it can no longer hold as 
vapor all the moisture it contains and some of it is deposited. Obviously 
the drier the air at a given temperature the farther must its temperature 
fall before the moisture is condensed. The dewpoint, or temperature 
at which condensation occurs, varies, then, with the absolute amount of 
moisture present in the air. 

As radiation proceeds from soil, vegetation and other substances 
it has been shown that the temperature of the air in the immediate 
neighborhood of these substances falls. In a calm this cooling frequently 
proceeds to the point at which moisture is condensed ; if this point is above 
the freezing point dew is formed; if below, frost is formed directly. It 
should be observed that frost is but an index of a low temperature and is 
not of itself injurious. It should be observed further that radiating sub- 
stances, particularly in a dry atmosphere, may cool the aij* several 
degrees below the freezing point without any deposit of frost. This is 
the black or dry frost. It is possible, too, for cooling to be extremely 
localized so that frost forms when the free air temperature is several 
degrees above freezing; frosts have occurred with a free air temperature of 
40°F. 

The condensation of moisture from the air sets free a certain amount 
of heat and retards the further fall in temperature. To that extent dew 
or even frost formation is beneficial as compared with low temperature 
without moisture condensation. It was formerly assumed that the 
liberation of heat from condensation would check any further tempera- 
ture fall and that because of this the dewpoint as determined the previous 
evening would forecast the minimum temperature of the night. Later 
investigations have shown this view to be unwarranted. 

Relation of Clouds and Wind to Frost Occurrence. — Evidently con- 
ditions favoring loss of heat by radiation and a calm condition of the air 
combine to produce dew or frost. Clouds reflect the heat lost by radiation 
and even radiate some of their own heat so that the passage of a cloud may 
for a short time raise the temperature a degree or two. Therefore cloudy 
nights, though still, are not very likely to be frosty. A fair breeze does 



342 



FUNDAMENTALS OF FRUIT PRODUCTION 



not prevent radiation but it mixes the air and prevents excessive cooling 
of any small portion of it; therefore, windy nights are not likely to be 
frosty. It is the nights which combine good radiation conditions with 
still air that the fruit grower should watch when his trees are in bloom. 

INFLUENCE OF LOCATION ON DANGER FROM FROST 

It has been shown that in the northern hemisphere the blossoming of 
fruit trees begins early in the south and, subject of course to minor dif- 
ferences, moves northward at a rate of 4 or 5 days for each degree of lati- 
tude, though somewhat more rapidly to the west of a given point than to 
the east. If the date of the last killing frost in the spring moved north- 
ward at the same rate, the calculation of the chances of a given fruit's 
escaping frost at any location would be a simple matter. Unfortunately 




Fig. 32. — The blossoming season of Wildgoose plum for 1898. (After Waugh 20 *) 



conditions are much more complicated. Dates of blossoming and of 
last frosts fluctuate from year to year. There are local variations 
particularly in the occurrence and severity of frosts; these are considered 
later. The present phase of the discussion is intended to point out that 
certain regions are more subject, perhaps, to late frosts at critical times 
for the fruit grower than other localities. 

The Blossoming Season and Latitude. — Figure 32 shows the dates of 
blossoming for the Wildgoose plum at various points in the United States 
for 1898, a season that was, on the whole, rather earlier than the average. 204 
Unfortunately not enough data are available for the construction of a 
map showing average blossoming seasons for any particular variety of 
fruit and minor fluctuations due to varying weather in different sections 



THE OCCURRENCE OF FROST 



343 



might change in another season the lines shown in the figure. However, 
the figure shows in a general way the northward progress of the blossom- 
ing season. 

Unpublished figures compiled by Phillips give average data for several 
kinds and varieties of fruits and show that the blossoming season moves 
northward more rapidly in the Mississippi valley than along the Atlantic 
seaboard (cf. Table 54). Phillips finds the rate for each degree of lati- 
tude to be: along the Atlantic coast, 5.7 days; in the Mississippi valley, 
4.8 days and for the Pacific region, 3.4 days. Somewhat similar relative 
progress has been found for certain phases of insect life. 95 These differ- 
ences between sections assume importance in connection with the dates 
of the last killing frosts. 

Table 54. — Average Date of Full Bloom for Several Fruits at Different 

Latitudes 

(After Phillips 1 ™) 



Latitude 


Pacific 
section 


Mississippi 
valley 


Atlantic 
section 


35° 


Mar. 11 


Mar. 16 


Mar. 19 


36° 


Mar. 14 


Mar. 16 


Mar. 24 


38° 


Mar. 19 


Mar. 30 


Apr. 10 


40° 


Mar. 18 


Apr. 11 


Apr. 19 


41° 


Mar. 22 


Apr. 19 


Apr. 26 


42° 


Mar. 27 


Apr. 27 


May 5 


Average all parallels 


Mar. 19 


Apr. 4 


Apr. 11 





Average Date of Last Spring Frost and Latitude. — The average dates 
of the last killing spring frosts are shown in Fig. 33. Though there is 
a general northward recession, local conditions evidently complicate 
this process in the extreme so that latitude alone is not a safe guide in 
determining the date of the last frost. The date lines of last frosts are 
obviously not parallel. As an example, the last-frost date line for 
June 1 is worth consideration. Barely dipping below the forty-fifth 
parallel in New England it leaves the United States to reappear in 
Minnesota where it remains well above the forty-fifth parallel until it 
leaves the states at the Canadian boundary. Entering the United 
States again in Montana it moves southward to New Mexico, almost 
to the thirty-fifth parallel, embracing a wide range of territory until it 
leaves Idaho, reappearing again in Washington. 

Average Dates and Frost Danger. — An average date, if the data on 
which it is based be sufficient to give it validity, means that approximately 
50 per cent, of the occurrences are prior to this date and 50 per cent. 



344 



FUNDAMENTALS OF FRUIT PRODUCTION 



follow it. If the average date of blossoming and the average date of 
the last frost for a given locality coincide there are possible four combi- 
nations of events: (1) blossoming before the average and frost before 
the average, a condition which may or may not be disastrous to fruit 
at that point; (2) blossoming before the average and frost later than 
the average, very likely to be a disastrous combination; (3) blossoming 
after the average date and frost before the average date, a safe condition, 
and (4) blossoming later than the average and frost after the average, 
unsafe. In cases 1 and 4 the last frost may or may not precede the 
blossoming, with chances balancing. Cases 2 and 3 balance each other. 



125° 120 



1 00° 95° 90° 85° BO 9 




Fig. 33. — Average dates of last killing frost in spring. (After Reed lb9 ) 

It appears, therefore, that locations where the average blossoming date 
and average last frost date coincide have an even chance of escaping 
frost, a margin of safety that is rather small for growing of the fruit 
in question. 

Determining Frost Risks in Different Sections and Localities. — Averages, 
of course, do not indicate the range of the figures that they represent. 
The range of last frost dates may be considerable at one point and limited 
at another, with the averages identical. Table 55 shows variations in 
the last frost dates on record for several stations with identical average 
date for this event. Such averages have only a limited significance for 
the fruit grower, unless the fruit he grows generally blossoms consider- 
ably later than the average date of the last frost. 

The last column in Table 55 records standard deviations from the 
average date of the last frost, Apr. 15 in each case. This standard 
deviation means, taking Roseburg for example, that over a considerable 



THE OCCURRENCE OF FROST 
Table 55. — Spring Frost Data for Selected Stations 160 



345 



Station 


Average 
date 


Last in 
9 to 10 years 


Last in 
1895 to 1914 


Standard 
deviation 


Keokuk, Iowa 

Cumberland, Md 

New Bedford, Mass 

Lebanon, Nev 

Roseburg, Ore 


Apr. 15 
Apr. 15 
Apr. 15 
Apr. 15 
Apr. 15 


Apr. 30 
May 2 
Apr. 28 
Apr. 15 
May 10 


May 4 

May 12 
May 2 
May 1 
May 10 


11.7 
13.0 
10.0 
12.4 
19.7 



period, in approximately half the years the last frost will occur between 
20 days before Apr. 15 and 20 days after, or between Mar. 27 and May 
5; in approximately one-fourth of these years it will occur before Mar. 27 
and in approximately one-fourth of the years it will occur after May 5. 
The record shows that the latest date of last frost for this station is 
May 10. Figure 34 shows the rather considerable range of standard 
deviations in dates of last frosts at various points in the United States. 




Fig. 34. — Standard deviations of dates of last killing frosts in spring. {After Reed 159 ) 

Of greater immediate value to the fruit grower is Fig. 35, showing 
dates "when the chance of killing frost falls to 1 in 10. " 159 If the average 
date of blossoming at a given point is identical with the date of the 1:10 
chance for that point the probability of damage is slight, being in fact 
\/ 2 x Ko = Mo, or one chance in 20. This may happen very frequently 
in cane fruits and grapes, though in most cases the average date for 
orchard fruits would precede that of the 1:10 chance. Comparison of 
such average blossoming dates as are available and of real validity shows 



346 



FUNDAMENTALS OF FRUIT PRODUCTION 



that very few orchard fruits have less than one chance in 10 of encoun- 
tering frost. 

The data here presented are introduced as suggestive rather than 
for their absolute value. As pointed out elsewhere, a frost recorded as 
"killing," though damaging to tender vegetation, may do little or no 
damage to fruit blossoms; similar data based on the last occurrence of 
30° or 29°F. would be of more direct value to the fruit grower. Neverthe- 
less the general liability of certain regions to frosts damaging to fruits 
holds true, whatever criterion be adopted, and though it would be hazard- 
ous to apply the present data unreservedly to any one point they serve 



125° 120" 115° 110° 105° 100° 95" 90° 85" 80" 75" 70" 65° 




Fig 



35. — Computed dates when the chance of killing frost falls to 1 in 10. After these 
dates killing frost will occur only 10 years in a century. (After Reed lb9 ) 



adequately for comparison between different points. Arranged on a 
slightly different basis and in conjunction with accurate blossoming 
charts, which are not available, they would have even greater value. 
At present only generalizations are possible. The tendency of blossoming 
to advance more rapidly in the central than in the Atlantic states and the 
irregularity in the recession of last frosts, with a general tendency toward 
faster recession on the Atlantic seaboard, makes a given fruit more 
liable to frost damage in the Mississippi valley region than on the 
Atlantic coast, if local variations do not intervene. 



INFLUENCE OF SITE ON MINIMUM TEMPERATURES 

The air in the neighborhood of radiating surfaces has been shown to be 
cooled by conduction and the air temperature on a still night to increase 
with distance from the surface. As the air in contact with radiating 



THE OCCURRENCE OF FROST 347 

surfaces cools it becomes more dense and tends to sink. It is then 
replaced by air somewhat warmer, probably for the most part flowing in 
from the same level, which air in turn cools and sinks. If the supply of 
relatively warm air be extensive enough and warm enough, the radiating 
surfaces may be kept from reaching the freezing point. This frequently 
happens on hillsides where the coolest air is continuously being pushed 
downward by air nearly as cool and warmer air is flowing in from the side. 
So much cool air may accumulate, however, that it fills a depression com- 
pletely and raises the level of warm air. The warm air may be raised 
so high above a given object that, as radiation proceeds, the replacing 
air has little heat to give up. It therefore fails to warm the surface 
sufficiently to prevent freezing. 122 Little replacement can be expected 
by warm air from above since it is lighter. 

However, other things being equal, the wider a valley the greater 
its area in proportion to its circumference ; consequently the reservoir 
of free warmer air at any level is greater in proportion to the radiating 
shoreline at that level. The higher levels, in a given valley, therefore, 
in addition to having better " drainage facilities" for removal of cold 
air have larger reservoirs of warm air on which they can draw. For 
the same reasons a slight elevation above a wide valley may be con- 
siderably freer from frost than a higher elevation above a more restricted 
valley. 

The term "air drainage," used to signify the resemblance of the 
flow of cold air to the flow of water, is more or less unscientific and 
inexact. 122 Nevertheless it is a convenient term; it suffices for practical 
purposes and doubtless will continue in use. In many cases there is 
an actual flow of air, closely comparable to the flow of water. This 
flow of air is frequently the salvation of orchards in narrow valleys 
which otherwise would fill quickly with cold air. 

In the discussion of Sites the statement is made that air drainage 
insuring as much freedom from spring frosts as possible is one of the 
most important considerations in picking the site for an orchard. It 
should be stated here conversely that the best method of insuring against 
frost and against the continual tax of frost-fighting is the proper selec- 
tion of a site. There are certain sections where to secure proper soil 
or plentiful moisture it becomes necessary for the prospective fruit 
grower to locate on low sites that are subject to frost. He should recog- 
nize clearly that he is exchanging relative immunity from frost for other 
advantages; the exchange may be profitable if the frosts are not too 
numerous and too severe. Over a large part of the country, however, 
a considerable latitude in choice is available and intelligent discrimi- 
nation in the choice of site may very easily make the difference between 
considerable profit and heavy loss. The grower who is forced to protect 
his orchard may make a profit in spite of his heavy overhead expense 



348 



FUNDAMENTALS OF FRUIT PRODUCTION 



and annual tax; the grower whose location is such that he is comparatively 
immune from spring frosts is more likely to be commercially successful. 

Sometimes the line that divides desirable and undesirable locations is very 
finely drawn. Table 56 shows minimum temperatures during the blossoming 
season at two locations not far apart and with only 25 feet difference in elevation. 
The dissimilarities in average minima are at once obvious. 

Table 56. — Minimum Temperatures at State College, New Mexico 

(After Garcia 71 ) 
(Station A 25 feet higher than Station B) 



Day 



March 



April 



1912 



1913 



1912 



1913 



1 

2 

3 

4 

5 

6 

7 

8 

9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 

Average. 



36.1 



30.5 



18.0 
20.0 
25.0 
41.0 
42.0 
30.0 
36.0 
32.0 
19.0 
21.0 
31.0 
35.0 



13.0 
16.5 
20.5 
35.0 
38.5 
27.0 
31.0 
26.5 
17.0 
19.0 
26.5 
31.5 



29.1 



25.2 



32.0 
38.0 
38.0 
49.0 
44.0 
39.0 
39.0 
40.0 
37.0 
52.0 
39.0 
41.0 
36.0 
32.0 
39.0 
40.0 
38.0 
39.0 
40.0 
49.0 
40.0 
31.0 
38.0 
51.0 
43.0 
34.0 
49.0 
44.0 
40.0 
48.0 



40.6 



24.5 
26.0 
33.0 
46.5 
45.0 
34.0 
36.0 
37.5 
34.5 
45.0 
34.0 
40.0 
33.0 
29.0 
34.0 
35.5 
32.5 
33.0 
34.0 
40.0 
35.0 
29.0 
33.0 
45.0 
39.0 
28.5 
40.0 
39.0 
35.5 
39.0 



35.7 



45.0 
40.0 
40.0 
34.0 
35.0 
51.0 
38.0 
36.0 
33.0 
38.0 
36.0 
29.0 
30.0 
31.0 
39.0 
38.0 
44.0 
49.0 
39.0 
59.0 
46.0 
53.0 
43.0 
31.0 
32.0 
36.0 
39.0 
40.0 
44.0 
44.0 



39.7 



42.0 
35.0 
36.5 
31.5 
31.5 
40.0 
36.0 
33.5 
30.5 
36.5 
35.5 
25.5 
27.0 
28.0 
35.0 
35.0 
40.0 
44.0 
35.0 
45.0 
44.0 
43.5 
42.0 
27.0 
29.0 
33.0 
35.0 
36.0 
40.0 
40.0 



35.7 



THE OCCURRENCE OF FROST 349 

More important, however, is the consideration that Station B during the 
time covered by these data registered temperatures below freezing 28 times as 
compared with 13 for Station A; Station B registered temperatures 28°F. or 
less 14 times while this point was reached at Station A, only five times. Ana- 
lyzing the figures in another way: in the spring of 1912 Station B had a minimum 
of practically 28°F. as late as Apr. 26 though Station A did not reach this figure 
during the season. In 1913 the last minimum of 28°F. or less for Station A 
occurred on Mar. 26 and for Station B the date was Apr. 14. 

Similar variations were found in Nevada between two points 190 feet apart 
and differing in elevation by 13.5 feet. 42 The average April and May minimum 
for the higher station was 42.7°F.; for the lower it was 39.5.° On selected single 
nights paired observations were 29-22, 34-31, 32-24, 39-31, 37-30. The diver- 
sity in the amount of fruit grown in 2 years on sites such as these, other 
things being equal, must necessarily be great and the difference in expense of 
orchard heating in the two cases would be well worth considering. 

In some cases this effect is said to be somewhat neutralized by the 
increased earliness of higher elevations. As a rule vegetation is later at 
high altitudes, but this condition is reversed frequently between points 
differing in altitude only a few hundred feet. An interval of 2 weeks 
between the first blossoming dates has been reported at points in Utah 
2 miles apart and with 200 feet difference in elevation. 2 It is not, how- 
ever, clear that this was due wholly to the elevation since slopes and 
condition of soil and of trees were not stated and the variations reported 
are certainly much more marked than is ordinarily the case, making 1 
day's difference for each 14 feet in elevation. Were the air constantly 
still, during the whole season up to blossoming, the moderately high 
elevations might indeed accumulate enough excess of heat to make con- 
siderable difference but in nature this condition obtains only during a 
very small portion of the time and such differences as do occur generally 
may be attributed to other effects. 

The steepness of slope necessary to effective freedom from frost varies 
with the local topography. Young 219 states: "From observations in 
the Pomona Valley, California, it appears that there is little if any advan- 
tage to be gained by locating on orchard in the upper portion of a long 
uniform slope of 150 feet or less to the mile. However, in even slight 
depressions of whatever shape or direction on this slope the frost hazard 
is likely to be considerably greater." 

MINOR FACTORS AFFECTING TEMPERATURE 

Of interest chiefly to growers of strawberries and cranberries are 
certain differences in narrowly restricted limits, differences usually small 
but frequently important. Included among these are those due to 
elevation, to the character of the soil covering and to the state of the soil. 
Minor Differences in Elevation. — Observations on three sets of ther- 
mometers at several points in Williamstown, Mass., with the upper 



350 



FUNDAMENTALS OF FRUIT PRODUCTION 



thermometers exposed at a height of 5.5 feet, the lower at 0.5 feet, show 
differences tabulated in Table 57, from which it appears that a strawberry 
plant may be exposed to considerably lower temperatures on a frosty 
night than the trees above it or than the thermometer in the ordinary 
shelter. Milham points out that the differences are greatest at the 
time of the minimum temperature and at the coldest station, in other 
words when conditions for frost are most favorable. Strawberry growers 
should bear this in mind in interpreting for their own use forecasts issued 
by the Weather Bureau. 

Table 57. — Temperature Differences with Height 134 
(Degrees Fahrenheit) 



Average difference . 
Largest difference. 



Station 1 



0.5 

2.0 



Station 8 
(8 p.m.) 



1.5 

4.0 



Station 7 



2.1 
5.0 



Station 1 



0.5 
2.0 



Station 8 
(minimum) 



2.0 
4.0 



Station 7 



2.9 
5.0 



On the other hand Cox 46 found temperatures at 5 inches above the 
soil lower than those at the surface, particularly on nights with good 
radiation conditions. 

"The average depression of temperature," he writes, "at the 5-inch height 
below that at the surface for the season of 1907 (May to October inclusive) was 
1°[F.]. The average depression on clear cool nights probably reached 4°. There 
were several instances of differences exceeding 6°." Cox evidently was not 
entirely satisfied with the possible explanations he advanced for this difference 
though they doubtless explain it in part. He states, "In a marsh grasses and 
uprights from the vines interfere slightly with radiation from the thermometers 
placed on the surface and it is probable that a thermometer or leaf exposed at an 
elevation above the surface loses its heat more rapidly by radiation than if it 
rested upon the surface because the upper one is not shielded in any way and 
while the radiation is going on from the lower one, at the same time heat is being 
conducted to it from the ground beneath. A thermometer resting upon the 
surface of the bog becomes a part of the soil or vegetation upon which it rests, 
as it were, and is benefited by the free conduction of heat to it from the ground, 
while the conduction to and through the air is very slight in comparison; because 
of these differences in radiation and conduction, the surface thermometer usually 
registers a higher temperature than the instrument a few inches above. For 
the same reason, the temperature of the vegetation at the surface and 5 inches 
above would vary as these temperatures have varied, especially when the surface 
vegetation is shielded above. It is a matter of common knowledge that in the 
bogs the cranberries growing at the tops of the uprights a few inches above the 
ground are often damaged by frost while those lying on or near the ground escape 
injury." 

Cox reports also two series of observations on temperatures at various 
heights up to 36 inches above the surface. On the bog the 5-inch height had 



THE OCCURRENCE OF FROST 



351 



the lowest average minimum temperature, the surface averaging 1.7° higher than 
the 5-inch level and 1.4° lower than the 36-inch level. In a garden on upland 
the differences were less. Cox summarizes his observations on this point as 
follows: "The temperature at 2.5 inches averaged lowest, 44.5°[F.], instead of at 
5 inches, as on the bog, but the difference was very slight between these two 
elevations — 0.1°. The surface thermometer averaged highest, 45.5° but there 
was only 1° difference on an average between the two extremes while the average 
surface reading was 0.6° higher than at 36 inches. The average for the entire 
season fairly represents the conditions prevailing each month, the highest in 
each case occurring at the surface and the lowest at 2.5 inches." Table 58, 
compiled from Cox's report, shows minima for nights selected because of the 
low temperatures and indicates no substantial variation from his averages. 46 

Table 58.— Minimum Temperatures in Open Over Sandy Loam 
(Degrees Fahrenheit) 



Date 


Sur- 


2.5 


5 


7.5 


10 


12 


15 


36 


(1907) 


face 


inches 


inches 


inches 


inches 


inches 


inches 


inches 


May 20 


24.9 


23.7 


23.8 


24.0 


24.8 


24.9 


25.0 


25.9 


May 21 


24.9 


22.9 


23.0 


23.1 


23.1 


23.1 


23.0 


23.8 


June 6 


34.7 


31.4 


31.5 


31.7 


31.7 


31.7 


31.2 


31.4 


Sept. 22 


28.0 


27.8 


27.8 


28.1 


28.3 


28.0 


28.2 


28.6 


Sept. 30 


25.0 


24.6 


24.7 


25.0 


25.2 


25.1 


25.2 


25.4 



It is evident that these differences are not constant. Some light is 
thrown on the effect of radiation by data compiled from Greenwich 
observations showing that a thermometer on grass fully exposed to the 
sky registered lower than a thermometer suspended 4 feet from the 
ground: 111 

Degrees 
fahrenheit 

On cloudless nights 9.3 

Half cloudy 7.3 

Principally cloudy 6.8 

Entirely cloudy 3.4 

Influence of Soil. — Reference is made again to Cox's work for data 
concerning the minimum temperatures over two different soils. Table 
59 shows minima for selected nights with the average for the month. 
The difference, striking at the surface, becomes very slight at 3 feet. The 
differences up to 5 inches are, however, of no little significance to the 
strawberry grower. They are to be regarded as due to character of the 
soils, since other conditions were uniform. Incidentally it may be stated 
that Cox considers it possible for identical atmospheric conditions to 
cause a light frost in the spring and not in the fall because of the difference 
in soil temperatures at the two seasons. To the extent that a high day 
temperature indicates considerable heat furnished the soil, it diminishes 

23 



352 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 59. — Minimum Temperatures in Open over Two Soils 46 
(September, 1906) 





Over peat 






Over sand 




Differences between peat 
and sand 


Day of month 






































Surface 


5 
inches 


36 
inches 


Surface 


5 
inches 


36 
inches 


Surface 


5 

inches 


36 
inches 


5 


38.4 


33.1 


34.8 


45.0 


35.9 


35.9 


-6.6 


-2.8 


-1.1 


14 


35.6 


33.0 


34.7 


43.9 


35.0 


35. 1 


-8.3 


-2.0 


-0.4 


24 


35.7 


32.5 


33.4 


41.0 


34.0 


33.5 


-5.3 


-1.5 


-0. 1 


27 


33.9 


31.0 


30.4 


40.3 


30.8 


30.3 


-6.4 


+ 0.2 


+ 0.1 


28 


39.8 


31.9 


35.7 


43.0 


35.7 


36.1 


-3.2 


-3.8 


-0.4 


30 


34.0 


28.8 


31.4 


39.6 


31.0 


33.0 


-5.6 


-2.2 


-1.6 


Monthly mean.. 


50.6 


47.0 


48.7 


53.6 


48.6 


49.0 


-3.0 


-1.6 


-0.3 



the probability of frost the following morning. Furthermore Cox states, 
"It is practically impossible for frost to occur in the bogs on the first cool 
night following a warm spell, but it is likely, if conditions are favorable, 
on the second night after the soil has become cold." 

The difference in temperature over the two soils is due probably to 
their difference in radiating and conducting powers. Peat absorbs and 
radiates heat readily but of course the heat lost by radiation warms the 
air exceedingly little; peat is a poor conductor and cannot warm the air 
greatly by conduction. The sand, though not as good an absorber of 
heat is a better conductor and warms the air above it at night. 

Influence of Soil Covering. — A thick mat of vegetation covering the 
soil prevents much heating during sunshine. At night, though it pre- 
vents conduction of heat from the soil, it radiates heat and thus tends to 
lower the air temperature further. It is not strange therefore that lower 
temperatures are found over vegetation than over bare ground. Table 

Table 60. — Temperatures Over Sod and Over Bare Ground 

(After Seeley 1 ™) 
(Degrees Fahrenheit) 




Loss 



Surface, bare ground 

Surface, sod 

Half inch below surface, bare ground 
Half inch below surface, sod 



17.7 
19.1 
16.1 
11.7 



60, giving the means of observations on 18 morning at Peoria, 111., shows 
the increase in difference of surface temperatures between sod and bare 
ground from afternoon to morning. The sod surface is 2° cooler in the 



THE OCCURRENCE OF FROST 



353 



afternoon and 3.4° cooler in the morning. Below the surface, however, 
the sod loses less. 

In minimum temperatures 5 inches above the surface on cranberry- 
bogs considerable difference, according to the density of the vegetation, 
is reported by Cox, 46 from observations made in September, 1906. Table 
61, which records his observations for the coldest nights, shows the magni- 
tude of these variations attributable to the difference in the amount of 
vegetation and the effect it has on soil temperature. Similar inequalities 
may be expected in very weedy and dense strawberry beds. More frost 
damage has been observed in weed-infested German vineyards than in 
those kept clean. 138 

Table 61. — Minimum Temperatures with Thick and with Thin Vegetation 

(After Cox 46 ) 
(Degrees Fahrenheit) 



Day of month 


Thinly vined 


Thickly vined 


Difference 


5 


33.1 


28.3 


-4.8 


14 


33.0 


28.8 


-4.2 


24 


32.5 


28.9 


-3.6 


27 


31.0 


24.4 


-6.6 


28 


31.9 


28.0 


-3.9 


30 


28.8 


23.0 


-5.8 


Monthly mean 


47.0 


43.6 


-3.4 



The effect of mulching, a common practice in strawberry growing, 
should be mentioned at this point. As a winter protection the value 
of a mulch is indubitable. In early spring a mulch tends to retard 
blossoming, an effect which may or may not be desirable. Once the 
plants are in blossom, however, a mulch may invite frost damage. 

Lazenby 103 reported observations to this effect: "To compare temperatures 
over mulched and unmulched ground I took 16 observations with a self-registering 
minimum thermometer daily between May 17 and June 1 of last year. The 
average minimum over straw was 43.2°; over bare ground 46.4.° The greatest 
difference was 7°. This year the average minimum over straw was 32.3°; over 
bare ground 34° with a maximum difference of 3.5°." 

This effect is due probably to the exclusion of sunshine from the 
soil during the day and to increased radiation at night. If the mulch 
is used to cover the plants during frost, its effect is, of course, totally 
different. 

Influence of Soil Moisture. — Observations on surface temperatures 
in wet and in dry sanded bogs at Berlin, Wis., in 1906, indicated a 
consistent and at times considerable, difference. Table 62, compiled 

23 



354 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 62. — Surface Minimum Temperatures on Dry and on Wet Sanded Bogs 

(Adapted from Cox i6 ) 
(Degrees Fahrenheit) 



Date 



ry sand 


Wet sand 


Difference 


43.9 


37.7 


-6.2 


41.0 


37.4 


-3.6 


40.3 


33.1 


-7.2 


43.0 


38.0 


-5.0 


39.6 


32.3 


-7.3 


35.8 


27.3 


-8.5 


53.6 


51.2 


-2.4 



Sept. 14 

Sept. 24 

Sept. 27 

Sept. 28 

Sept. 30 

Oct. 1 

September mean 



by the selection of the coldest nights, shows that at the very time when 
these differences are most important they are greatest. It might be 
argued that the wet sand was coldest because it had given up more 
heat; however it is stated that on Oct. 1 cranberries in this bog were 
frozen, except in the dry sanded section. The lower minimum on the 
wet sand is attributed to the heat lost in evaporation at the surface. 
It should be remarked that irrigation with relatively warm water 
at the time of frost apparently has proved of considerable value occa- 
sionally but irrigation that merely wets the soil and keeps it cold is 
probably injurious. An experimental investigation in Wisconsin showed 
very little difference in temperature over irrigated and over unirrigated 
blocks. 

King, 102 commenting on the results, stated: "Not only did frost form after 
the water was brought to the areas but some of the rape leaves became stiff 
with streams of water flowing both sides of the row. It is true, however, that a 
very perceptible difference could be noted in the degree of stiffness which foliage 
took on above and close to the water, and that which was more distant. For 
close to the water the leaves did not become so rigid as to break in the hand while 
at a distance from the water they did. 

"It is quite possible that were broad areas irrigated at such times the pro- 
tection would be more marked, but it does not look very hopeful for the protec- 
tion against night frosts by this method, especially where the temperature falls 
3 or 4° below freezing." 

It seems evident from the data above that evaporation does not 
interfere with radiation sufficiently to offset its cooling effect and that 
unless the water actually imparts heat it is deleterious. A thoroughly 
saturated soil is, however, likely to retard frost formation. 

Cox 47 states: "The explanation is found in the high specific heat of water. 
A certain quantity of heat lost during the night time from relatively dry ground 
and its vegetable cover cools the exposed portions of these poor heat-conducting 



THE OCCURRENCE OF FROST 



355 



objects to a very low temperature. An equal loss of heat from the same sub- 
stances when they are loaded with moisture results in only a small lowering of the 
temperature not only because the water must now be cooled in addition to the 
ground and vegetation but, as we know, water requires the removal of consider- 
able heat to cool it slightly. The radiation losses from the saturated surfaces 
may also be less than from the dry surfaces." 

Evidently looseness in application of terms "wet" and "dry" has 
led to some apparently conflicting results. Petit 149 records observations 
that at first seem contradictory to those of Cox, since they indicate 
higher temperatures over the wetter soil (c/. Tables, 63 and 64). Petit 

Table 63. — Temperatures in Moist and Dry Soils 

{After Petit 149 ) 
(Degrees Centigrade) 



Date and time 



Dry soil 



Saturated soil 



Apr. 23, 4.00 p.m 
Apr. 23, 7.15 p.m 
Apr. 24, 5.20 p.m 



29.7 

18.5 

3.9 



21.6 

16.1 

6.5 



states that the chief cooling influence in wet soil, evaporation, is inactive 
at night, that the moist soil conducts heat more rapidly than the dry 
and therefore can receive more heat from below; he evidently considers 
that these factors offset the greater radiation he ascribes to wet soil and 
the lower heat storage during the day. Curiously enough he finds 
that dew forms earlier and is more abundant on the moist soil. It is 
possible, however, that Cox and Petit worked with soils of different 
texture and moisture content and that their results are not necessarily 
conflicting. 

Table 64. — Surface Temperatures Over Wet and Over Dry Soils 

(After Petit 149 ) 
(Degrees Centigrade) 



Date 



Time 



Not watered 



Watered 



Sept. 23 
Sept. 23 
Sept. 23 
Sept. 24 
Sept. 28 
Sept. 28 
Sept. 29 



4.30 p.m. 
6.00 p.m. 
10.00 p.m. 
5.00 a.m. 
5. 15 p.m. 
9.25 p.m. 
5.55 a.m. 



18.2 
14.0 
6.9 
2.3 
10.6 
5.6 
4.0 



15.6 
12.4 
7.3 
3.2 
10.6 
6.9 
5.2 



Effect of Cultivation. — In a series of observations on the minimum 
temperatures over cultivated and uncultivated soils at Peoria, 111., it 



356 



FUNDAMENTALS OF FRUIT PRODUCTION 



was found that cultivation apparently increased the temperature about 
2°. 175 Cox states: "It is as important to cultivate as it is to practice 
drainage," but adds that "it is impossible to determine absolutely the 
advantage in exact degrees gained by cultivation, draining or sanding. " 
It is evident that his statement refers to any attempt to make the 
observed differences fit all cases. 

Cultivation is said by Petit to increase the loss from the surface of 
the soil by radiation, diminishing heat conduction from below; tamping 
the soil is stated to lessen this danger. It should be observed that the 
temperatures recorded are those of the surface and not of the air above. 

Table 65. — Temperatures at Surface op Cultivated and Packed Soils 

(After Petit 149 ) 
(Degrees Centigrade) 



Date and time 


Packed 


Stirred 


Lumps 


July 15, 1898 — 1 . 30 p.m 


16.8 


37.9 

17.8 
14.2 


37.4 


July 15, 1898— 8. 15 p.m 

Aug. 4, 1898—8 . 00 p.m 


15.8 
12.6 



Increased surface of the loosened soil would tend to increase the loss 
of heat by conduction and might easily raise the temperature of the air 
immediately above it, though the surface itself be cooled. 

Significance — Particularly in Small Fruit Culture. — A saving of 
2° or 3° may or may not be an important matter according to circum- 
stances and consequently any one of the factors affecting temperature 
may in itself be important. However, it is frequently the case that 
several of them are operative at once and their combined effect is likely 
to be considerable, particularly on nights when these differences are 
most important. 

Cox expresses this aptly : " While there is an average difference of 3.4° . . . 
between the minimum thermometers in the thinly vined and the heavily vined 
sections, a difference of 2.4° . . . between the minimum thermometers on 
peat and sanded bogs, both thinly vined, and a difference of 2.2° between the 
surface and 5 inches, it is obvious why an average difference of 10° . . . can 
exist between a minimum thermometer exposed at the most favorable location 
as far as drainage and sanding and cultivating are concerned and another in a 
most unfavorable location, an unsanded peat section with a very dense growth 
of vegetation, and poor drainage. [The greatest difference observed by Cox 
was 17.1°F.] It is not strange therefore that in a bog where there is a variation 
in the conditions of sanding, draining, and cultivation, the range in minimum 
temperatures is considerable, and that a portion of a bog is seriously injured by 
frost while another portion completely escapes." 46 

These inequalities are extremely localized; probably none of them is 



THE OCCURRENCE OF FROST 357 

effective at the height of trees and they are of little importance to the 
orchardist. They are, however, of extreme importance to the grower of 
small fruits. His is the most difficult problem in heating his fruit planta- 
tion but, on the other hand, he can do more than any other fruit grower to 
prevent frost. Generally he has the same freedom as the orchardist in 
the selection of site; in addition he can take advantage of minor localized 
variations. In aiming to profit by them he is following cultural prac- 
tices that are beneficial to his fruit plants in other ways. 

Summary. — Spring frost is important in setting geographic limits to 
the commercial culture of. fruits of some kinds and in determining the 
regularity of crops, yields and profits in practically all deciduous fruit 
growing sections. Frost formation depends to a considerable extent on 
the radiation of heat by exposed surfaces during the night. Because of 
radiation on still clear nights, temperatures close to the earth are lower 
than those at somewhat greater elevations, giving rise to the condition 
known as temperature inversion. On account of radiation the real tem- 
peratures of plants may be several degrees lower than those registered by 
sheltered thermometers. When the dewpoint is very low, freezing will 
occur without frost formation. Clouds and wind both protect against 
frost, the former by reducing the total effect of radiation, the latter by 
mixing warm air with that which has been cooled. In a general way 
both the blossoming dates of fruits and the average dates of the last 
killing frosts range later with each increase in latitude, though the prog- 
ress of the two is not always parallel. Study of Weather Bureau records 
showing average last dates of killing frosts, together with the standard 
deviations therefrom, will make possible an accurate determination of 
frost danger beyond any particular date for any given locality, though not 
for any site. Air drainage secured by suitable elevation is of considerable 
importance in determining danger from frost in particular sites. Minor 
differences in temperature within narrow limits in space are occasioned by 
minor differences in elevation, amount of soil moisture, character of the 
soil covering, type of soil and system of cultivation. These are seldom 
important in influencing frost injury to tree fruits; however, they may be 
of considerable importance in small fruit culture. 



CHAPTER XX 

PROTECTION AGAINST FROST 

The fruit grower should have, not only knowledge of the conditions 
under which frost occurs, but information as to the exact danger points for 
his various fruits and as to the value of different protective measures that 
may be at his 'disposal. 

CRITICAL TEMPERATURES 

If heating is to be done it should be delayed until the temperature is 
near the critical point to save expense and exhaustion of the fuel in the 
heaters before morning. If it is known that the blossoms of one variety 
or of one species are more tender than others protective effort may be 
concentrated more or less on the tender plants. At times it has been 
assumed arbitrarily that a certain temperature is fatal and that because 
certain orchards had been exposed to that temperature they would bear 
no crop. Accordingly the calyx spray was omitted, to save labor and 
expense, only to have it appear later that a fair crop had survived the freeze 
but had become thoroughly infested by codling moth, scab and other 
pests. If, then, there is a certain temperature that is universally fatal 
to the blossoms of all fruits or of one kind of fruit it should be known. 

A compilation of temperatures stated as dangerous to blossoms of 
various fruits is reproduced here as Table 66. 

The considerable difference in the damaging points as stated by these 
various writers is significant and it seems probable that the range of 
killing temperatures is as great if not greater than indicated by the table; 
West and Edlefsen state that there is sometimes a spread of 5°< The 
variations in temperatures between sheltered thermometers, exposed 
thermometers and plant tissues make field observations of only limited 
value. Variations in radiation conditions make the correction of ther- 
mometer readings to plant temperatures uncertain. Furthermore, 
different blossoms must be exposed to radiation in varying degrees because 
of diversity in their positions in the cluster and on the branch. 

Assuming, however, that temperatures can be measured accurately, 
as doubtless has been done in closely controlled work such as that of 
Chandler and of West and Edlefsen, the final result is still a complex 
involving several factors whose separate measurement is difficult. 
Several blossoms, alike in development, will show differences in their 

35S 



PROTECTION AGAINST FROST 



359 



Table 66. — A List of "Danger Points" as Given by Different Authors 

Degrees Fahrenheit 
(After West and Edlefsen, 207 with additions) 





Closed but. 








Fruits 


showing 


In blossom 


Setting 


Authority 




color 








Apples 


27 


29 


30 


1 




27 


29 


30 


2 




27 


29 


30 


3 




25 


28 


28 


4 




25 


28 


28 


5 




25 


28 


29 


6 


Peaches 


20 
29 


25 
30 


28 
30 


1 




3 




29 


30 


30 


2 




22 


28 


28 


4 




25 


27 


27 


5 




25 


26 


28 


6 


Cherries 


22 
29 


28 
30 


29 
30 


1 




2 




22 


28 


28 


4 




25 


28 


30 


6 


Pears 


27 


29 


29 


1 ' 




29 


29 


29 


2 




28 


29 


29 


3 




25 


28 


28 


4 




25 


28 


30 


6 


Plums 


30 
30 


31 
30 


31 
31 


1 




2 




30 


31 


31 


3 




22 


28 


28 


4 




25 


28 


30 


6 


Apricots 


30 


31 


32 


2 




30 


31 


32 


3 




22 


28 


28 


4 




25 


27 


30 


6 


Prunes 


30 


31 


31 


2 




30 


31 


31 


3 




28 


29 


30 


6 


Almonds 


26 


27 


30 


7 


Grapes 


30 


31 


31 


7 



Authorities: (1) Wilson, W. M. 216 (2) O'Gara, P. J. 141 
(4) Paddock and Whipple. 143 (5) W. H. Chandler. 38 
(7) Young, Floyd D. 218 



(3) W. H. Hammon. 71 
(6) Garcia and Rigney. 71 



resistance to the same freezing; different trees of the same variety will 
set materially different crops; finally, varieties are unequally susceptible. 
It is impossible at present to state to what extent fruit blossoms are 



360 FUNDAMENTALS OF FRUIT PRODUCTION 

or can be supercooled, at what temperature ice formation occurs or at 
what temperature damage results. General sudden freezing following 
supercooling is considered in itself injurious. 152 To what extent this 
applies to fruit blossoms cannot be stated at present. Indeed it is possible 
that under natural conditions supercooling as ordinarily understood 
does not occur in fruit blossoms. The influence of capillarity on freezing 
in these tissues cannot be stated now. It is, however, safe to conclude 
that critical temperatures as determined by laboratory methods would 
be somewhat lower than would appear from field observations with ordi- 
nary thermometer exposures, because of the differences between air 
temperatures and plant temperatures under the radiation conditions 
accompanying most frosts. For the same reason precise determination 
of killing points would not be of direct application in the orchard. Paren- 
thetically it may be remarked that the insufficient recognition of radia- 
tion effects on plant tissues in horticultural investigation may account 
for many of the conflicting results secured. 

However, studies in artificial- freezing are interesting, though the 
high degree of humidity that accompanies them is not invariably present 
in nature. This high humidity may serve conceivably to inoculate 
the plants with freezing nuclei and cause freezing at higher temperature 
than would be required in a drier atmosphere. Despite limitations, 
however, the tests by artificial freezing possess considerable significance. 
West and Edlefsen have reported some rather extended investigations 
of this sort. 

In part, they summarize their results as follows: "Ben Davis apple buds in 
full bloom have experienced temperatures of 25, 26, and 27°F. without injury, 
but 28° usually killed about one-fifth. Twenty-nine degrees or above are safe 
temperatures. Twenty-five degrees kills about one-half and 22° about nine- 
tenths. On several occasions, however, apples matured on branches that experi- 
enced 20° when the buds were in full bloom. 

"With Elberta peach buds in full bloom, 29°F. or above are the safe tem- 
peratures, because even though occasionally 26, 27, and 28° do no damage, yet 
on most occasions 28° will kill from one-fourth to one-half. Twenty-six degrees 
kills about one-half of them and 22° about nine-tenths. Temperatures as low 
as 18° have failed to kill all of them. 

"With sweet cherry buds in full bloom, 30°F. is the safe temperature; 25, 26, 
27, 28° have done no damage, but 29° usually kills about one-fifth. Twenty- 
five degrees usually kills about one-half, and when the buds were showing color 
22° killed only two-fifths of the buds. 

"Sour cherries are hardier than the sweet varieties. When the buds were 
showing color 23°F. did not harm them, and when they were in full bloom 26° 
killed about one-fifth and 22° only two-fifths of them. 

"With apricots, 29°F. is the safe temperature; 26 and 27° killed about one- 
fifth and 22° killed one-half. . . . 

"The foregoing figures refer to the buds when in full bloom. Starting from 



PROTECTION AGAINST FROST 



361 



this stage, the earlier the stage of development the hardier the buds are; and in 
general, when the fruit is setting the injury is from 5 to 10 per cent, more than 
when they are in full bloom. 

"Sour cherries are the hardiest, and then follow in order apples, peaches, 
apricots, and sweet cherries." 208 

Field observations sometimes indicate that open peach blossoms are 
more resistant than apple blossoms at the same stage. 

At Different Stages of Blossom Development. — Table 66 indicates 
that the difference in tenderness of blossoms at various stages in their 
development is well recognized. Table 67, arranged from a similar table 
by West and Edlefsen, shows experimental data that are, in general, 
confirmatory. 

Table 67. — Hardiness of Jonathan Apple Buds to Various Degrees of Arti- 
ficial Cooling 207 



Date 


Stage of 
blossom 


Duration of 
freezing, 
minutes 


Temperature, 

degrees 

Fahrenheit 


Percentage 
damaged 


April 25 


Full bloom 
Full bloom 
Full bloom 
Full bloom 
Fruit setting 
Fruit setting 
Fruit setting 
Fruit setting 
Fruit setting 
Fruit setting 
Fruit setting 


10 

5 

45 

5 

25 

5 

5 

20 

30 

15 

5 


24.5 
26.5 
27.5 
28.5 
28.0 
25.5 
26.5 
26.5 
27.5 
27.5 
27.5 


52 


April 29 


36 


April 25 

April 29 


54.0 



May 9 

May 9 

Mav 9 


46.0 
93.0 
40 


May 10 

May 10. : 

May 9 

May 9 


22.5 
21.0 
59.0 
62.0 



It should be remembered that not all the blossoms on a tree are going 
through the same stage of development at any given time and the amount 
of damage done by a light to moderate frost will depend to a considerable 
extent on the number of opened and of unopened buds. This is shown 
in Table 68. 

Strawberries that are half grown, however, appear able to stand 
more freezing than the blossoms. 

Coit 43 reports on this fruit: "Blossoms are injured by temperatures below 
30° at the ground but young fruit endures temperatures as low as 24° at the 
ground and 28° in a government shelter without injury and green fruit protected 
by foliage endures temperatures several degrees below this. Ripening fruit 
endures less cold, being injured by temperatures below 25° at the ground. A 
good picking was taken from Excelsior plants Dec. 24, 1903, although the mercury 
had fallen at the ground to 22 to 26° during 10 nights of the month. Some 



362 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 68. — Percentage op Open and op Unopened Blossoms Killed by the 

Freeze op Apr. 4, 1908 (24°F.) 

(After Chandler 39 ) 



Variety 


Buds open 


Buds unopened 


Oldmixon Free 

Oldmixon Free 

Elberta 

Elberta 


69.9 
25.4 
24.4 
51.1 


36.6 

15.3 

7.1 

1.1 



green fruit well protected with foliage survived January, 1904, the mercury falling 
to 14 at the ground one night, 16 one night, 17 two nights, 18 one night and 19 
three nights; and a few berries ripened during the early part of the month." 

Varietal Differences. — Varietal differences in hardiness are sometimes 
apparent in apples. 

In one case in Missouri the greatest injury in Jonathan seemed to be in the 
stamens while in Oldenburg the pistil was damaged. It may be suggested that 
this type of injury might have some interesting bearing on the pollination of 
mixed orchards. 

In Iowa many of the Russian varieties were hardier in blossom than standard 
varieties in better locations. Similarly among the native plums a freeze that 
killed the ovaries of several varieties such as Rollingstone which, incidentally, 
is very resistant to winter cold, injured only a part of the blossoms of De Soto, 
Cheney and other varieties. These in turn were surpassed in resistance by the 
Russian plums which were said to have been "less exposed than our native 
plums." 28 The Bosc pear has been reported as more tender in blossom than the 
other pears. 218 Chandler states that among peaches " the large flowered varieties 
seemed uniformly to be the most hardy, probably because the petals remained 
closed over the pistils longer." 37 This statement was in reference to resistance 
to frosts at blossoming time; after that period no determining factor could be 
found. Elberta, tender at some other stages, seemed to resist very late frosts as 
well as most varieties. 

Some varieties of strawberry are more susceptible to frost injury 
than others because their flower stalks are longer and more inclined to 
raise the blossoms above the protection of the leaves. 5 

Schuster 174 reports on the Ettersburg No. 121 strawberry: "The first blos- 
soms being below the foliage are quite well protected from ordinary frost. Foli- 
age protection is quite a factor when comparing this variety with other varieties 
of light foliage, as the primary blossoms are very apt to be fully protected during 
the frost, while the secondary blossoms that extend beyond the foliage will 
usually be frosted. Due to the extended blossoming period, it will take repeated 
frosts to destroy the crop unless there is a heavy freeze." 

Some interesting studies have been made in an attempt to correlate 
varietal morphological peculiarities with differences in hardiness. 



PROTECTION AGAINST FROST 363 

Emery, 62 in Montana, found injury in strawberry varieties ranging from 12 
per cent, to zero. The date of bloom in this case seems to have had little effect, 
since Warfield, one of the earliest blossoming of the 58 varieties under observa- 
tion, escaped all injury. Wilcox 215 at the same station found the anthers of 
certain varieties injured by frost; the tissue in which the pollen grains were 
embedded ruptured and a small proportion of the pollen grains were killed. Some 
injury was observed in styles and stigmas, probably enough to interfere with 
their functioning. In blossoms which had been fertilized the injury was confined 
to the akenes; in no case was the receptacle injured. The akenes became dis- 
colored rapidly. In resistant varieties they were so deeply imbedded in their 
pits as to be practically surrounded by the pulp. Tender varieties had their 
akenes most exposed or in very shallow depressions. Between these extremes 
there was a regular gradation. It thus seems possible that a variety may be 
resistant at one stage — before fertilization, for example — and yet be tender at 
another stage, say, after fertilization. 

Vigor and Recuperative Ability. — The vigor of the tree is stated 
frequently to be a factor in the damage produced by frost. This opinion 
may be founded on observations of the crop the weak trees bear and in 
failure to recognize that, frost or no frost, such trees fail often to set a 
large percentage of fruit. A series of freezings of blossoms from strong 
and from weak Gano apple trees indicated no superior hardiness in blos- 
soms from the more vigorous; in fact the average of the various tests 
was very slightly in favor of the weak trees. 38 In herbaceous plants, 
injury sometimes appears more pronounced in those making a less 
vigorous growth, but in all probability the observed difference is due 
to the superior recuperative powers of the more vigorous plants. There 
is some indication that plants treated with nitrate of soda recover from 
frost damage better than others. This recovery is, however, in the vege- 
tative portions. There is, occasionally, a fairly large second bloom on 
apple and pear trees following a frost, but this is the exception and ap- 
parently it is not related to vegetative vigor. Recuperative power is of 
little immediate benefit to the. grower once the blossoms are killed. 

Weather Conditions Before and After Freezing. — The weather pre- 
ceding and immediately following the freeze may be factors of some 
little importance. 

Pfeffer 151 , speaking of plant tissues in general, says: "The resistance to 
cold depends to a certain extent upon the present and previous external 
conditions. Thus Haberlandt found that seedlings grown at 18° to 20°C. 
froze more readily than those grown at 8°C." Rosa 162 found that cabbage 
grown in a greenhouse at 20°C. killed when exposed to -4°C. for 1 hour 
while plants grown in a cold frame were uninjured by exposure to the same 
temperature for over 2 hours. It seems reasonable to suppose that the 
same principle applies to fruit blossoms. Garcia 71 records that a temperature 
of 24.75°F. at 2 a.m. followed by a rise to 31° at 5:30 caused less than 3 per 
cent, injury to Alexander peach blossoms which were in full bloom at the time, 



364 FUNDAMENTALS OF FRUIT PRODUCTION 

though in other instances considerable damage followed a temperature of 25.5°. 
It should be recalled that there is practical unanimity among investigators that 
rapid thawing is not in itself injurious, but there is no evidence as to the effects 
of light on frozen tissue. Light is known to increase permeability and may well 
be conceived to prevent the return to the cells of water which has been withdrawn 
upon freezing, thus causing injury to tissues which otherwise would recover 
their normal state. The common conviction among practical horticulturists 
that rapid thawing is injurious may be founded on observations of the effect 
of -light on frozen tissue. Furthermore, the effects of the duration of exposure to 
a given temperature have not been established definitely. 

Signs of Damage. — The thermometer, evidently, frequently fails to 
give close or reliable indication of the amount of damage a frost has 
inflicted. A fairly close estimate may be made, ordinarily, late in the 
forenoon following a freeze, by an examination of the buds themselves. 

The pistils are the parts most readily affected in the blossom, becoming, when 
damaged, wilted and discolored, though the bud may unfold its petals and 
stamens. Curiously, in April, 1920, at Columbia, Mo., a temperature of 14°F. 
when Jonathan apple blossoms were fairly well advanced seemed to damage, not 
the pistils, but the stamens which turned orange in color, and the effects also be- 
came evident on the stems near the purse. A similar condition, though less 
pronounced, has been observed in the Willamette valley in Oregon. Sometimes 
the petals are dwarfed but the bud otherwise uninjured. In peaches advanced 
beyond the blossoming stage, Chandler 38 states that the veins surrounding the 
seed are the most tender, followed in order by the kernel and the flesh. Chandler 
suggests that the greater tenderness of the seed may be correlated with the differ- 
ence in sap density. The young seeds of the apple seem particularly tender and 
after a frost they frequently are brown while the flesh is apparently undamaged. 

Paddock and Whipple 145 state that after fertilization has occurred apple 
blossoms may survive some injury to the seeds though blossoms of the stone 
fruits frozen to the extent that the basal part of the pistil is damaged rarely set 
fruit. When interior apple tissues outside the seed cavities are damaged the 
fruit does not mature. In this particular case, they say, the injury becomes 
apparent early, in a yellowing of the tissues around the stem end of the fruit. 
Seedless apples, particularly of some varieties, frequently develop to maturity 
but generally are somewhat smaller than those with seeds. The same writers 
state that the pear will mature fruit after showing still more injury than the 
apple. In the young fruit they find much the same conditions holding, though 
the stone fruits are said not to show injury which is confined to the seed cavity 
until the time of the final swelling just before ripening, when the injured fruit 
will show gummy exudations and ripen abnormally or it may drop before ripen- 
ing. When the injury is more extensive they drop shortly after blossoming. Apples 
and pears survive injury to the seeds alone and in most cases with no other visible 
evidence of damage. Apples injured outside the seed cavity do not mature but 
pears so injured develop abnormally through enlargement of what would ordi- 
narily be the neck of the fruit. This enlargement, together with the retarded 
development of the parts surrounding the core, results in the familiar " bullneck." 



PROTECTION AGAINST FROST 365 

Injury to pear flesh apparently must extend well away from the core to prevent 
the development of the fruit, though it conceivably may interfere to some extent 
with the so-called "secondary effect" of pollination. 

Impaired germination of pollen of pear, plum, cherry and peach on 
exposure for 6 hours to a temperature of — 1.5°C. has been reported. 167 
Chandler 38 found that pollen of the Jonathan apple after exposure to 
— 3°C. showed a germination of 33 per cent, as compared with 84 per 
cent, for unfrozen pollen, and pollen of the Cillagos apple frozen for 
30 minutes at — 8°C. germinated 25 per cent, as compared with 67 per 
cent, for unfrozen. 

Frost Injury and the Size of the Crop. — Finally it must be considered 
that the damage from a given frost is a varying quantity. Some peach 
trees on which 1,000 peaches would be a good crop bear 20,000 or more 
fruit buds. Obviously, with other conditions favorable, a loss of 80 
per cent of the buds would not interfere with the production of a full 
crop and in a commercial sense this frost would not prove damaging. 
If, however, the same trees were bearing only 8,000 buds a loss of 80 per 
cent might become a serious matter. 

It should be apparent that no set rules of procedure as governed by 
observed temperatures can be given. Probably the safest course for the 
grower when freezing occurs is to try to keep the temperature above 
29°F. if he is heating his orchard and after a frost it is best to proceed on 
the assumption of a full crop unless the evidence to the contrary is 
convincing. 

AVOIDING FROST THROUGH LATE BLOSSOMING VARIETIES 

The relatively wide range in blossoming dates of the many kinds and 
varieties of fruits is often important in determining the relative danger 
from frost to an orchard on a given site. Conversely, the blossoming 
dates should have bearing on the decision as to the type of fruit to be 
planted. On a very large scale the limiting factor in the growth of 
apricots and almonds is not their lack of hardiness to winter cold, since 
some varieties are probably as hardy as, or even hardier than, the peach, 
but rather their extremely early blooming. 

Blossoming Range Varies with Earliness. — The earlier the average 
date of blossoming in any section the longer is the spread of the ordinary 
season of bloom. In the north the time between the first peach and the 
last apple to blossom is frequently shorter than the interval in the south 
between the first and the last peach. Consequently the relative earliness 
or lateness in blossoming of a variety may be more important in some 
regions than in others. Table 69 shows the difference between peaches 
and apples in the number of times heating might be necessary at various 
places in Utah. The difference between a total of 263 heatings for the 



366 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 69. — Number of Heatings Necessary to Protect Utah Orchards 
{After West and Edlefsen 20 ' 1 ) 



County 


Number 
of years 


Peach 


Apple 


Apricot 


Cherry 


Utah (Provo) 

Provo Bench 

Box Elder (Corinne) .... 
Salt Lake (Salt Lake) .... 

Weber 

Cache 


16 
16 
14 
16 
13 
16 


93.0 
28.0 
32.0 
36.0 
66.0 
8.0 


46.0 

13.0 

8.0 

15.0 

4.0 

3.0 


45.0 

45.0 
3.2 


21.0 






Totals 


263.0 
2.9 


89.0 
0.97 


21.0 


Average per vear 


1.5 



peaches and 89 for the apples would make a considerable item in the 
cost of production. In addition, the later blooming fruit is not only- 
likely to encounter fewer frosts but such as it does encounter are likely 
to be less severe. Finally, it should be recalled that the later stages of a 
blossom's development are the most tender; for this reason also a given 
frost is likely to damage the early variety more. This double effect is 
well shown in Table 70. 

Table 70. — Percentage of Peach Blossoms Killed by Temperature of 28°F. 

{After Garcia 11 ) 



Varieties 



Fruits just 
setting 



Freshly opened 
flowers 



Buds about to 
open 



Elberta 

Crothers 

Salway 

Texas King ... . 
Hynes' Surprise 
Alexander 



97 
95 
87 
86 
91 
91 



66 
73 

72 



45 
47 
56 



This table shows that for blossoms just setting fruit there was not 
enough difference to indicate any varietal superiority in hardiness. How- 
ever, Elberta, Crothers and Salway blossoms were all at the most ad- 
vanced stage which is very tender. The three other varieties had a 
considerable number of blossoms less advanced at the time of the freeze 
so that, despite a rather large percentage of killing, the fruit of these 
varieties had to be thinned, while the first three varieties bore very little, 
Elberta in fact bearing none at all. 

Table 71 is based on the Mikesell data, 133 with additions. Though computed 
rather arbitrarily it shows in a general way the relative susceptibility to frost 



PROTECTION AGAINST FROST 



367 



Table 71. — Date of First Blossoms Relative to Last Minimum of 29°F. at 
Wauseon, Ohio, for 30 Years 



Blossoming relative 
to frost 



Apple, 
years 





, 


Pear, 


Peach, 


years 


years 


11 


13 


19 


14 


13 


13 


17 


14 


12 


12 


18 


15 



Plum, 
years 



Cherry, 


Grape, 


Straw- 
berry, 


years 


years 


years 



Red 
rasp- 
berry, 
years 



Type variety: 

Before 

After 

Early variety 

Before 

After 

Late variety: 

Before .... 

After 




15 
14 



11 

IS 



14 





10 


15 


26 


16 


15 







14 


26 




14 







15 


26 







26 




26 




20 



at Wauseon of the fruits under observation there (see Type fruits). In addition 
an attempt is made to show how earlier or later blossoming varieties of the respec- 
tive fruits would have been affected. A somewhat artificial method was 
necessary. Taking as guide the average blossoming dates of various fruits at 
Geneva, N. Y., 90 the varieties studied in Table 70 were interpolated and the 
differences between their average dates of blossoming at Geneva and that of the 
earliest and latest blossoming common varieties grown there were used in the 
Wauseon figures. Thus the apple was figured on the basis of Gravenstein being 
2 days earlier in blossoming than the type variety (King). The Bartlett pear 
was fitted into the New York tables on the assumption that it blossomed with 
Clapp Favorite and Angouleme; Anjou and Vermont Beauty were the extremes, 
2 days earlier and later respectively. The plum (variety not stated) was placed 
in the middle of the Domestica group. 

The table should not be taken too literally as it is constructed on such arbi- 
trary assumptions (including the temperature selected as injurious). Neverthe- 
less it shows quite clearly the respective chances of frost damage to different 
fruits at a given spot in northern latitudes and in a measure the relative import- 
ance of early and late blossoming varieties which is much greater in some fruits 
than in others. Furthermore, it should be understood clearly that the blossoming 
dates of all kinds and varieties of fruits have a much wider spread in milder 
climates than that of the northeast and these differences are much greater and 
more important in these regions. 

Figure 36 shows the blossoming dates of certain fruits in relation to 
the last spring temperature of 27°F. at a point in southern Utah. In no 
year did the apricot or the almond blossom after the last temperature of 
27°, and in no case did the Yellow Transparent, generally a rather early 
blossoming apple, bloom before. Between these extremes lie the Elberta 
peach, which blossomed after the last 27° temperature in 2 years out of 
the 8 represented, and the German prune which preceded it in 1 year 
out of 6 recorded. The likelihood of damage or safety from frost is this 
locality quite evidently depends on the kind of fruit chosen, more so 



368 



FUNDAMENTALS OF FRUIT PRODUCTION 



than in sections where the blossoming season has less spread. At Geneva, 
N. Y., the average interval from the first peach blossom to the last 
apple tree's first bloom is 15 days. However, there are unquestionably 
years in almost any fruit growing region when the blossoming period 
actually determines the difference between a full or a partial crop — or a 
crop failure. 




Fig. 36.— Frost susceptibility of several fruits as determined by date of blossoming. 

(After Ballantyne 11 ) 

Blossoming Period and Fruit Bud Position. — In addition to varietal 
difference in blossoming season there is occasionally some diversity within 
the variety. There is a tendency, though it is by no means constant, for 
vigorous trees to blossom somewhat later; sometimes the interval 
between vigorous and weak trees is 2 to 3 days. Terminal and lateral fruit 
buds of apple frequently are several days behind the spur fruit buds in 
opening; in at least one instance Jonathan trees have lost practically all 
the spur blossoms from frost and still returned a partial crop from 
their terminal buds. The outer buds on long twigs and all buds on short 
twigs in peaches are the first to open and the slight difference in develop- 
ment of these and the basal blossoms on the same trees has made at times 
a vast difference in the crop borne in respective zones. 38 

Retarding Blossoming. — Attempts at retarding fruit blossoms so they 
will escape a certain amount of exposure to frost have not proved success- 
ful on a commercial scale. Whitewashing the branches to reduce the 
amount of heat absorbed from sunlight has been discussed previously; 
shading has been shown to have only a very limited application. Despite 
abundant evidence to the contrary the notion persists that mulching 
retards the opening of fruit buds. Except for fruits whose tops are 
covered, as strawberries, it is of no value. 



PROTECTION AGAINST FROST 



369 



If late blooming is urgently needed it is best secured by selecting late 
blossoming varieties, planting them on a north slope and keeping them 
growing vigorously. The last two measures are effective only within 
comparatively narrow limits, leaving the first as the best method of 
evading frost damage. In certain fruits the present varietal range in 
blossoming season is hardly sufficient to secure protection through the 
selection of the later blooming sorts, but in others practical immunity 
from damage may be obtained in that way. There is reason to believe 
that late blooming varieties of many fruits may be bred and the ultimate 
solution of the frost problem lies in that direction. 

Indices to Blossoming Periods in New Location. — Sometimes in 
considering locations where fruit has not been grown it is desirable to 
know at what time the trees may be expected to bloom. It is possible 
that phenological observations on native plants in different sections 
would show a degree of correspondence with the various fruits so that 
certain native plants might serve as indicators of what fruit trees would 
do in the same locality. 

Figure 37, arranged from the Mikesell Records, 133 shows the overlapping of 
the King apple in the stage from first blossom to full bloom with poison ivy, a 



1884- 




































































I88fe 




































































l»»8 




































































1890 







































































l»y<! 




































































1894 




































































189G 




































































1898 
























/ 


1899 


























— 1 


PP 


-F 





20 11 24 t& ?6 30 E 4 6 8 10 12 14 1& 18 20 22 
April M a y 

Fig. 37.— Comparable phenological stages in apple and poison ivy- (Apple from first 
blossom to full bloom; poison ivy from starting of buds to first fully formed leaf). 

fairly common wild plant, in the stage from buds starting to the first fully formed 
leaf. It will be observed that the correspondence, though not invariable, is 
rather close. Some plants show better correspondence with the King apple than 
others; several recorded in the Mikesell records show less than the poison ivy. 
This instance is but suggestive of many other parallels or overlappings in 
blossoming seasons that may be established — parallels that in many cases would 
repay careful study. 



FROST PREDICTION 



It is frequently important to know a few hours in advance whether 
or not a frost will occur, so that final preparations for protection against 



370 FUNDAMENTALS OF FRUIT PRODUCTION 

its effects may be made. In a general way frost may be looked for on a 
clear, still night; clear, because it favors radiation, still, because the cooled 
air is not mixed with the warmer air. These conditions are associated 
with high barometric pressure. However, they do not always produce 
frost and a closer estimate is desirable. 

Relation of Dewpoint to Minimum Temperature. — Until recently the 
dewpoint as determined in late afternoon or early evening has been 
considered to mark the minimum temperature for the following morning. 
Air contains varying percentages of moisture; the higher the tempera- 
ture the more it can carry as vapor. If any given sample of air is cooled 
the point is reached ultimately where some of the moisture is deposited. 
This is the dewpoint. The condensation of moisture releases heat to the 
air and it was thought that the heat thus released was sufficient to prevent 
any further drop in temperature and that the evening dewpoint therefore 
marked the minimum for the following morning. 

Careful comparison of indicated and actual temperatures has shown, 
however, that the afternoon or evening dewpoint alone is not a suffi- 
ciently reliable indicator to be of any great value in predicting the 
minimum for the following morning. In fact Cox 46 records a slight degree 
of frost with the humidity at 100 per cent. Ordinarily, however, it may 
be assumed that when the evening relative humidity is from 40 to 50 
per cent., the ensuing minimum temperature on a characteristic radiation 
night will be very close to the evening dewpoint; when the evening relative 
humidity is below 40 per cent the minimum will average 5° above the 
evening dewpoint; with evening relative humidities above 50 per cent 
the minimum temperatures will be below the evening dewpoint. 

Little reliance can be placed on the afternoon maximum alone as an 
indicator unless it is very high indeed. No maximum below 75 or 
76°F. should be regarded as a guarantee against frost the following morning. 

Weather Bureau Methods. — At present no one method of predicting 
minimum temperatures is in use by Weather Bureau officials throughout 
the country. Local conditions apparently make a certain method fit 
closely at one point while at another point it gives less satisfactory results. 
It seems probable that observations extending over at least 2 years for 
each section should be accumulated and the data studied to determine 
which method will give the closest approximation in future predictions. 

Smith 182 has devised several methods and applied them to data from different 
points. The simplest, perhaps, is the so-called median temperature method. 
This is based on the assumption that, in weather characteristic of most spring 
frosts, the "radiation nights," clear and rather still, the temperature falls practi- 
cally at a uniform rate from a maximum in the afternoon to a minimum in the 
morning and that the times of maximum and minimum temperatures will be 
the same for all such days. The average time of the median, half way between 
the times of the maximum and of the minimum, is ascertained from previous 






PROTECTION AGAINST FROST 371 

records of the particular station. A thermometer reading at this median time, 
subtracted from the afternoon maximum, gives, presumably, half the total 
fall in temperature to be expected. Thus if the maximum were 70°F., the 
median temperature 50°, the difference, 20°, taken from the median temperature, 
would indicate the expected minimum to be 30°. Under conditions obtaining 
at some stations this method seems the most reliable that has been tried. 
In general it seems to give closer approximations to actual temperatures in 
regions of very low humidity, not, perhaps, because the method works better 
there than elsewhere, but possibly because the other methods do not work so 
well. As indicated by Hallinbeck, with certain precautions in its application 
it seems to work well at Roswell, New Mexico. Wherever compared with 
the older method of assuming identity between evening dewpoint and morning 
minimum it has proved superior. 

Still more accurate predictions were found possible in Ohio by Smith, using 
the equation y = a + bR, where R is the evening relative humidity, y the varia- 
tion of the morning minimum temperature from the evening dewpoint, while a 
and b are constants derived from previous data accumulated at points with like 
conditions. This linear equation, when plotted, fitted the Ohio data very satis- 
factorily, but charts from certain other points were fitted more closely by a 
parabola whose equation was modified by Smith to read v = x + by + cz in 
which x, y and z are coefficients to be determined from previous data, b the eve- 
ning relative humidity, c the square of the relative humidity and v the variation 
of the minimum temperature of the following morning from the evening dew- 
point. The value found for v is added to or subtracted from the evening dew- 
point and the minimum temperature indicated. 

The method of obtaining the constants is explained in detail in Supplement 
16 of the Monthly Weather Review. As has been suggested above, the constants 
vary with the locality. As samples, the following may be cited: for the y = a 
+ bR equation, at Lansing, Mich., a — —11.2, b = 0.727, at Grand Junction, 
Col., a = —7.01, b = 0.53; for the v = x + cz -\- by equation, Modena, Utah 
(all nights, radiation or otherwise), x = 7.3, y = 0.18, z = 0.0057; for Montrose, 
Col., x = -22.0, y = 0.383, z = 0.01167. 

The first equation has been found to give satisfactory results at some places, 
the second has proved preferable at others; as stated above, the median tempera- 
ture method seems best here and there, while in some cases still other methods 
are used. Sometimes a mean between results secured by two methods has 
proved more nearly accurate than either singly. One disadvantage of the 
median temperature method as compared with the others outlined here lies in 
the fact that the forecast cannot be made until several hours later than is possible 
from the metheds based on hygrometric data. The fact that different methods 
fit various places is probably an expression of the differences in topography and 
in humidity, relation to centers of high pressure and other factors somewhat 
peculiar to particular localities but all combining in frost production. 

It should be borne in mind also that the methods outlined fit only 
radiation nights and that occasionally fruit blossoms are damaged by 
cold in other ways such as high cold winds or cold snow squalls. To 
forecast these, reliance must be placed in the weather map. The problem 



372 



FUNDAMENTALS OF FRUIT PRODUCTION 



is, in any case, sufficiently complex to warrant the grower who wishes 
reliable forecasts in trying to secure them from the nearest station of the 
Weather Bureau, either directly or by corrections from forecasts made 
for some nearby point. 

Local Interpretation of "Key Station" Predictions. — It will be under- 
stood, considering the local differences in temperature, that the general 
forecast may require correction for the grower's own site. The forecast, 
as issued, is based upon observations from sheltered instruments at 
a certain spot; yet it is given out necessarily to cover a wide radius of 
territory where local differences may be considerable. Districts that 
are well organized for frost fighting have several "key stations" for which 
the forecasts are corrected individually. Even in such cases, however, it 
may be necessary to make discriminating corrections if the probable 
minimum for a given spot is to be determined. 

Table 72 shows minimum temperatures on cold spring mornings at 5.5 
feet and 0.5 foot elevations at three spots in the village of Williamstown, Mass. 
Station A is a shelter thermometer and may be considered the "key station." 
It is of interest to see how predictions for the key station would apply to straw- 
berries at Station 7. As is shown in the last column of the table the difference is 
variable but always considerable, under conditions favorable to frost. As 
Milham, 134 from whose data the table is taken, states, it is not a difference due 
to site alone; in adapting the forecast for Station A to vegetation at Station 
7 allowances must be made as follows: 2° for the deviation between sheltered 
and exposed thermometers, 3° for the inequality in height of the two thermome- 
ters above ground and 6° for the difference in site. These together indicate a 

Table 72. — Minimum Temperatures at Williamstown, Mass. 134 





Station A 
(shelter) 


Station 1 


Station 8 


Station 7 


Difference, 
Station A 
and lower 7 


Date 


Upper 


Lower 


Upper 


Lower 


Upper 


Lower 


1907 

April 27 

May 1 

May 5 

May 11 

May 12 

May 20 


32 
33 
38 
27 
42 
37 
39 
33 
37 

40 
39 
35 
42 
46 
39 
42 
40 


29 
36 
25 
41 
35 
38 
31 
36 

38 
37 
33 
30 
45 
39 
40 
39 


30 
28 
34 
24 
40 
35 
38 
30 
36 

38 
36 
33 
30 
44 
39 
40 
39 


30 
28 
32 

39 
34 
36 

34 

37 
35 
31 
28 
43 
38 
38 
39 


27 
25 
32 

36 
32 
34 

32 

36 

32 
30 
27 
39 
37 
36 
37 


27 
25 
31 
18 
33 
34 
36 
25 
31 

35 
31 
31 
28 
40 
38 
36 
36 


23 
21 
27 
15 
31 
31 
33 
20 
31 

34 

28 
27 
24 
35 
38 
34 
34 


9 
12 
11 
12 
11 

6 


May 21 

May 24 

May 28 

1908 
April 29 


6 

13 

6 

6 


May 1 

May 3 

May 5 

May 9 

May 10 


11 
8 
18 
11 
1 
8 
6 















PROTECTION AGAINST FROST 373 

total of 11° which, it is evident from the table, was realized frequently. Though 
it is unsafe to generalize from a few observations, it is interesting to note that 
for the lower temperatures at Station A the departures for Station 7 averaged 
greater than they did for the higher temperatures at Station A ; in other words it 
would seem that as the temperature at Station A came nearer to the freezing 
point the temperature at Station 7 was in even greater measure more likely 
to drop below that point. Evidently a strawberry grower at Station 7 should 
deduct at least 1 1° from the minimum indicated for Station A to forecast the 
probable temperature at his own place; if apples were the crop at the same point 
the deduction would be somewhat less. 

Even greater differences are reported by Cox 46 between minima on the bog 
at Mather, Wis., and the minima at the "key station" La Crosse, 55 miles away. 
Shelter minimum temperatures on the upland at Mather for May, 1907, averaged 
3.8° below those at La Crosse with ranges from —14° to +8°; minima at 5 
inches above the bog at Mather averaged —8.5° below those for La Crosse, 
with ranges from —20° to +5°. Cox states that the average difference when the 
weather is clear and the pressure high is about 18°, so that in such weather a 
minimum of 50° for La Crosse signifies a bog minimum at Mather of about 32°. 

The grower who wishes to prophesy with accuracy what the minimum 
will be in his own orchard, bog or field must rely on the Weather Bureau 
to furnish information as to the probable minimum at some fixed point 
and he must rely on himself to adapt these indications to the spot where 
his own crop is located. To do this it will be necessary to keep accurate 
records of minima at his own orchard on all clear nights during the spring 
for 2 or 3 years, to compare them with the records of the Weather Bureau 
and from these data to determine the probable and the safe corrections 
to be made. 

FROST FIGHTING 

The data already discussed show that much can be accomplished in 
combatting frost by selection of site, fruit and variety and in some cases 
by cultural practices. All these measures may be regarded as preventive. 
There remain for consideration the palliative measures. 

Smoke Screens to Reduce Radiation. — In view of the emphasis placed 
on radiation as a factor under frost conditions, efforts to prevent heat 
loss through radiation might be expected to be fruitful. In fact it is 
rather generally assumed that a dense smoke will so retard radiation 
losses that frost damage will be checked or prevented. Such cases have 
been recorded. However, quantitative data available for comparison of 
temperatures in smudged areas where the heating factor is eliminated 
with those in unsmudged and unheated areas do not indicate a sufficient 
saving of heat to make the smudge in itself of any great value. Table 73 
shows temperatures in a smudged area and in an unsmudged area adja- 
cent, in a German vineyard. The averages include some figures not 
presented here. 



374 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 73. — Temperatures in Smudged and Unsmudged Areas 138 
(Degrees Centigrade) 





Temperature 


Hour 












Smudged 


Unsmudged 


10:30 


• +2.01 


+ 1.87 


11:30 


+ 1.53 


+ 1.40 


12:30 


+0.78 


+0.62 


1:30 


+0.13 


+0.07 


2:30 


-0.73 


-0.50 


3:30 


-0.90 


-0.95 


4:30 


-1.14 


-1.25 


5:30 


-0.05 


-0.03 


Average 


0.098 


0.042 



The differences are at the most too small to be of practical impor- 
tance. It was suggested that the small difference was due to air move- 
ment and the investigator appears not to have been convinced that 
greater differences might not be found under other conditions. 

Kimball and Young, 101 using a pyrogeometer, measured the radiation 
in smudged and in unsmudged areas in California and Oregon, finding 
decreases by smudging from 0.110 and 0.115 calories per minute per 
square centimeter to averages of 0.098 and 0.103 respectively in Cali- 
fornia and in Medford, Oregon, from 0.109 to an average of 0.099. Con- 
siderable fluctuation under the smoke occurred, the maximum decrease 
amounting to 28 per cent, with averages respectively of 11, 10 and 9 
per cent. They conclude from their investigations that "the retardation 
of nocturnal radiation by the smoke cloud plays an insignificant part in 
frost protection." 

The reflection of heat from smoke clouds is evidently very small. 
Muller-Thurgau 138 points out that smoke differs in its composition from 
clouds. It should be recalled that radiation is constantly occurring, 
clouds or no clouds, and that they do not prevent radiation but only 
reflect heat, and since outgoing and incoming heat approach equal value 
on cloudy nights the net loss by radiation is small. Smoke differs from 
water vapor in being relatively transparent to long heat waves. There 
is a relatively large difference in the way violet (or blue) and yellow (or 
red) are transmitted through dust in the air — for example, the sun is 
yellow or red at horizon, the short waves not being transmitted as readily 
as the longer yellow and red waves. The sun looks red through smoke, 
showing the same effect. The smoke screen appears opaque because the 
eye uses the shorter waves but it must be very much less opaque to the 
long waves which the earth radiates. 



PROTECTION AGAINST FROST 375 

Covering and Spraying. — The protection of plants from frost by 
covering them with paper or cloth is of course effected through saving 
of the heat otherwise lost through radiation. The efficacy of this 
method is well known though it is not practicable in the orchard. 126 An 
experiment in California showed that with an outside minimum of 19° 
the lowest temperature under a paper covering spread over an almond 
tree was 24°, a saving equal to the raise in temperature secured in many 
instances by orchard heating. 

The protective effects of water spray were investigated in Utah by 
keeping a block of apricots under a continuous fine spray during a frost. 207 
Ice formed on the blossoms and it finally appeared that only the sprayed 
trees were damaged. The injury was not a mere failure to set fruit; 
there was actual killing. In view of the work of Harvey 87 it seems prob- 
able that in this case the ice formation on the surfaces of the blossoms 
inoculated the inside tissues with ice crystals and actually hastened their 
freezing. 

Orchard Heating. — The most successful results so far achieved in pre- 
venting low temperatures have been realized by the use of large numbers 
of small heaters, warming the air itself. This practice has become a 
settled part of orchard routine in some sections; in others it has been in 
extensive use but is now almost obsolete. There can be no doubt of 
its efficacy in some cases. Frequently, however, it has been considered 
too expensive insurance. The heating capacity of a set of heaters is 
limited and sometimes in a severe freeze the temperature sinks so low 
they are unable to maintain a protecting temperature, or in some cases 
a high cold wind renders them useless. On the other hand, a few degrees 
of freezing rarely destroys a whole crop. The full value of these heaters 
is, then, realized only with minima in a certain narrow range; with 
minima outside, they are either unnecessary or useless. 

It is probable that failure to realize these limitations led to the instal- 
lation, during the greatest vogue, of orchard heating equipment in many 
places where its true usefulness is rarely available and that failure to 
realize its limitations at the outset caused unjustifiable expectations of 
its value. In either case the reaction was bound to cloud the instances 
and circumstances in which it can be of real worth. 

Furthermore, orchard heating has been invoked at times when the 
difficulty, supposedly frost, was in reality something entirely different. 
At one time many cherry growers at The Dalles, in Oregon, installed 
extensive heating equipment to induce a proper setting of fruit when 
their orchards were of self sterile and inter-sterile varieties and what 
they actually needed was provision for proper cross pollination. Orchard 
heating cannot make weak trees set heavy crops. In view of the equal 
influence of freezing on blossoms of weak and of strong trees, as cited 
previously in this section, the increases sometimes reported in fruit set 



376 FUNDAMENTALS OF FRUIT PRODUCTION 

after frost on nitrate-fertilized trees may constitute a splendid testimonial 
for nitrate fertilization but they do not in themselves indicate that 
orchard heating without fertilization would have been beneficial. 

Heat Units in the Fuel. — Limits must be recognized to the amount of 
actual heating any ordinary equipment can secure. 

McAdie 127 indicates this in some interesting calculations. "At the present 
time," he states, "with a hundred burners to the acre, using a gallon each of oil, 
something like 15,000,000 British thermal units or 3,760,000 [kilogram] calories 
would be given off, provided the combustion was perfect, which of course is never 
true. Now, to raise the temperature of the air 1°F. over an acre to a height of 15 
feet is practically heating 653,400 cubic feet of air. In practice it is found that to 
maintain the temperature on a still night 1° above the freezing temperature 
requires 0.252 calories per hour per cubic foot. Therefore for a period of 7 
hours, which is about the average duration of a low temperature [McAdie wrote 
in California], although 10 hours is a safer period, there will be required 1,138,200 
calories. And if a raise of 5° is required it is evident that more than 5,500,000 
calories are needed or more than the full number of heat units in the fuel under 
perfect combustion." 

In practice oil is burned generally at a faster rate than that used in 
McAdie's calculations, but the published results of careful experiments 
indicate that the actual heating achieved rarely exceeds 5° and that 4° 
is a liberal estimate of what may be expected with ordinarily favorable 
conditions. A breeze of 6 miles an hour materially lowers the net gain 
of heat; any movement lowers it somewhat and dead calms are rare. 
According to Young, in the lard-pail type of heaters only about 40 per 
cent of the heat in the oil is actually realized in combustion and even 
in the high stack type it is doubtful if more than 70 or 80 per cent of 
its fuel value is attained. A still further loss is caused by the height of 
the "ceiling layer" of air which, though variable, permits in any case 
the accumulation of heat at a height above the trees. 

Height of the "Ceiling Layer." — The holding of heated air within a 
few feet of the ground appears mysterious unless the inversion of tem- 
perature be considered. Data introduced previously have shown that 
the normal adiabatic cooling of the air upward from the earth, charac- 
teristic of daytime, is modified during radiation nights and that the air 
only a few feet above the ground is distinctly warmer than that at or 
near the surface. It is this layer of warm air, acting as a roof or ceiling, 
that makes possible the warming of the air at the level of the trees. 
As the warmed air ascends from the heaters it mixes with other some- 
what cooler air and the mixture finally reaches a layer of the same tem- 
perature; it then has no impulse to rise further. 

Figure 38, by Humphreys, 97 shows a typical frosty morning tempera- 
ture gradient and is used by him to indicate how heat may be wasted. 
He shows that under the given conditions any portion of the surface 



PROTECTION AGAINST FROST 



311 



air warmed from 32 to 34°F. would rise to about 30 feet only, as shown 
by the adiabatic curve from 34°, until it would reach the layer of air 
having a temperature equal to its own. If it were warmed to 40°, 
however, it must rise over 250 feet, cooling somewhat by diminished 
pressure, until it reaches air with an equal temperature. Thus in one 
case the ceiling is about 30 feet high, in the other it is 250 feet high. When 
the gradient begins at, say, 24° instead of 32°, in other words when the 



1000 



900 



800 



700 



600 



.£ 500 

c 
o 



O 400 



300 



200 



100 















\ 


\ 


















\ 


















\ 


















\ 


















1 








71 
TEM 


'PICA 
°ERA1 


L MO 
UPE 1 


RNIhJ 
NVER. 


3 

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\ 
















»S 


\ / 








\ 




— c*t 




J^ 




> 
,\o 






\ 
\ 

\ 


^ 


l^ 













39 



40 



41 



32 33 34- 35 3G 3T 38 

Temp era+u re,d eg.fahr. 

Fig. 38. — Illustrating the physical possibility of protecting outdoors from frost by artificial 
heating. (After Humphreys 97 ) 



outside unheated surface air is at 24°, whether or not the gradient is 
affected at 500 feet, the ceiling above the 34° mark is raised, meaning 
that not only must the air now be heated from 24 to 34°, 10 degrees 
instead of 2, but a greater amount of air must be heated. The increasing 
difficulty of heating toward morning is due evidently to other factors 
besides the heaters themselves. 

If a few large fires are employed the body of warmed air rising from 
them is so great that it does not become mixed readily and rises farther 



378 FUNDAMENTALS OF FRUIT PRODUCTION 

than the heat from the small fires, being thus rendered ineffective in 
warming the air at lower levels. Large fires of course emit a considerable 
amount of radiation heat which warms the surfaces exposed, but since 
the intensity of heating by radiation diminishes as the square of the 
distance from the source of heat it soon becomes ineffective. In addi- 
tion the current set up above the large fire draws in the colder surface 
air to replace the warmed air driven high aloft and it is easy to conceive 
that it may disturb ceiling layers considerably. 

Effect of Wind. — Winds, besides carrying heat away directly, break 
up the "ceiling layer" of warm air and unless the heated areas are very 
large and the wind such that the warmed air is "blown down," they 
make heating efforts of little avail. Windbreaks, therefore, though at 
times they may invite frost conditions, may render heating more effec- 
tive, though they cannot preserve the ceiling layer which is necessary 
for full realization of its possibilities. 

Humphreys, 97 assuming a radiation per minute per square centimeter of 
0.1 calorie and evidently basing his calculations on soil surface area alone, 
disregarding vegetative surfaces, concluded that for each plot of ground 10 
meters by 10 meters there would be needed per hour 6,000,000 calories, which, 
assigning a value of 8,500 calories per gram of petroleum, indicates the need of 
approximately a pint and a half of oil per hour to offset radiation or to hold the 
temperature from falling. If a moderate air movement occur, new air must be 
warmed constantly. Humphreys, assuming the dewpoint below 32°, land sur- 
face horizontal, temperature of air 32° and a wind of 2J£ miles per hour (approxi- 
mately 1 meter per second), with air weight 1,290 grams per cubic meter, makes 
an interesting calculation of the amount of heat necessary to warm the entering 
air 2°C. to an elevation of 12 meters. He states: "Now the specific heat of the 
atmosphere is very approximately 0.24. Hence to warm 1 cubic meter of the 
given air 1°C. requires about 310 calories. Hence, to warm the air 2°C. to an 
elevation of 12 meters, as it enters the given area with the given velocity of 1 
meter per second, will require, per linear meter at right angles to its direction, 
approximately 2 X 12 X 310 X 7,440 calories per second, or the consumption of, 
roughly, 3.7 liters or 6.5 pints of oil per hour." 

A considerable amount of the heat imparted to the air as it enters is retained 
while the air drifts through the orchard; therefore, though radiation must be 
fought equally at all points the raising of air temperature itself is moic properly 
done on the windward edge. With the somewhat idealized conditions enumer- 
ated above, assuming an orchard 1 kilometer square (about 247 acres) with the 
breeze at right angles to one side the oil requirements are stated by Humphreys : 
to counteract radiation 8,600 liters; to warm the entering air 3,700 liters. A rec- 
tangular orchard might require more or less oil to warm the entering air, accord- 
ing to the direction of the breeze and if the breeze is quartering two sides must be 
warmed, but the amount to offset radiation alone is constant. In other words 
the oil necessary to offset radiation is determined by area alone ; the amount nec- 
essary to warm entering air is determined by the outline of the orchard and by 
the direction and velocity of the wind. 



PROTECTION AGAINST FROST 379 

Concerning the influence of wind velocity Humphreys says: "Of course a 
greater wind velocity than 2}-i miles per hour, the velocity above assumed, would 
appear to necessitate a correspondingly larger consumption of fuel for the border 
or entrance heating. But this, presumably, is not true in practice, since probably 
even this velocity, certainly a greater one, would considerably mix the surface- 
cooled air with the warmer air above, and thereby decrease the amount of 
necessary heating. During a perfect calm the required border heating is zero; 
it is also zero when there is a fairly good breeze and hence has its maximum value 
at some quite moderate intermediate velocity." 

It should be noted that Humphreys is stating that the higher the 
velocity of the air movement the higher the air temperature is likely to be. 
This is quite different from the case of high wind at a dangerous tem- 
perature, for here the heating required increases with the wind velocity 
and too many times becomes impossible. 

The choice of heater types depends on the nature of the service 
required. In some sections where dangerous temperatures are of 
short duration the simple 1-gallon heaters will be adequate; in other 
sections longer burning may be required. Young 218 points out that the 
size of the temperature inversion characteristic of many of the California 
frosts permits the use of stack heaters which, perhaps, could not be 
employed in sections where the temperature inversion is weaker. No 
one type is best for all sections or for all occasions in one section. 

Conditions Determining Practicability. — No general discussion can 
decide the question whether orchard heating is profitable. The con- 
tinuance of the practice in certain sections over a long period is rather 
good evidence that with conditions as they are in those sections it is 
either profitable or necessary or both. The necessity of the practice, 
if fruit is to be grown in a certain spot, ma}' mean that it is desirable or it 
may mean that the spot should be devoted to some other crop. If the 
value per acre of the crop is high, as with oranges, heating may be 
economically sound; if the value per acre of the crop is low, heating is 
of doubtful wisdom. If a given spot is exposed to several frosts a year 
heating is likely to pay as compared with no heating but it may be that 
fruit growing should be abandoned at that spot. 

The installation of an orchard heating equipment involves a heavy 
overhead expense. Each year heaters and fuel must be distributed and 
made ready. The chief difference in expense between a frosty and a 
frostless spring so far as heating is concerned is in the oil consumed and a 
reduction or increase in the labor charge. The profits of the frostless 
season are taxed only somewhat less than those of the frosty season. 
Frequently the yearly expense has amounted to $20 per acre; it has 
reached $40. In many, if not in most, fruit growing sections, $40 per 
acre added to the initial price of the land will secure sites located advan- 
tageously enough to escape this tax. 



380 FUNDAMENTALS OF FRUIT PRODUCTION 

Orchard heating is not so common as it was some years ago. Certain 
sections have abandoned it altogether, in others only a few growers 
continue it. In some instances too much has been expected of it; in 
others the falling in fruit prices from an artificial level has been a con- 
tributing cause, but probably in the majority of cases it has been aban- 
doned for the excellent reason that it has not paid. 

It will be seen from the Wauseon figures that heating at that point 
would be an expensive insurance considering the number of times it 
would be useful. If, in addition, the orchards are, as is the case fre- 
quently, bearing chiefly in alternate years, the likelihood of heating being 
profitable over a long term is further reduced. Assuming a damaging 
frost in half the blossoming seasons, a ratio far greater than that for the 
largest apple growing sections, and assuming a crop in alternate years, 
the chance of heating being required to save a crop is ^ X M or 1 in 
4. If damaging frost occurs once in 3 years the chance is Y% X }^ or 
1 in 6. At Wauseon, with very liberal allowance, it is, for the King 
apple, 2 in 15. It is significant that much of the experimental work on 
orchard heating has been done at temperatures above freezing because 
there was not enough frosty weather for all the tests. There are, too, 
in almost all sections, springs when the crop is damaged by high cold 
winds, under such conditions that heating fails to protect it sufficiently. 
If a season of this kind is added to seasons when heating is unnecessary 
the number of years when it really pays is still further reduced. 

The fruit grower is forced, sooner or later, consciously or uncon- 
sciously, to consider the economic doctrine of marginal utility. This 
means, as applied to the topic under discussion, that until all the land 
otherwise well adapted to fruit growing and free from frost danger in a 
given area is in use for that purpose it is of doubtful expediency to attempt 
fruit growing on land that will require heating. It means, too, that in 
seasons when profits in general run low they are, other things equal, 
wiped out first on the land that requires heating. 

In addition to the doctrine of marginal utility the grower should 
apply to his analysis the law of the minimum. Orchard heating is 
not likely to be profitable to him if his spraying is defective, his pruning 
poorly done, his land lacking in drainage or irrigation, his trees weak or 
if his fruit is not marketed to advantage. "When he is satisfied that he has 
developed these essentials so that none of them is limiting his profits and 
that frost is the limiting factor he can consider orchard heating. In some 
cases it will be profitable; in more cases it will not. 

FROST EFFECTS 

Manifestations of frost injury aside from the dropping of the fruit 
are sometimes found. The so-called bull-necked pears previously men- 
tioned are rather common and are sometimes confused with seedless 



PROTECTION AGAINST FROST 381 

fruit, particularly with that arising from late bloom. Russet bands, 
generally extending more or less completely around the middle of the 
fruit, though sometimes near the calyx end, occur on pears and occasion- 
ally on apples. Similar russeted areas, frequently somewhat raised, but 
less regular in location, are found on plums. Apples and pears with this 
form of injury are said to wilt rather rapidly. 144 

In the apple the outside leaves of a cluster sometimes show a form 
of injury called "frost-blister." 143 As observed in New Hampshire and 
Missouri, this injury does not appear to reduce the size of the affected 
leaves which are normally small and it apparently does not extend beyond 
the first two or three leaves to unfold. The injury evidently may occur 
when the buds are still very little advanced. The appearance is suffi- 
ciently described by the name; the "blisters" are caused by the separa- 
tion of the upper and the lower surfaces. The leaves tend to curl and 
in many cases drop off. Inasmuch as those most affected are of doubtful 
importance to the growing spur this type of injury is probably 
unimportant. 

Another interesting consequence of frost injury is the so-called 
"secondary bloom." When there is extensive killing of fruit buds the 
spurs which have bloomed may form new blossoms, which in some cases 
have been observed to mature fruit, sometimes with and sometimes 
without seeds. The same phenomenon may occur independently of any 
frost. It is discussed more fully under Fruiting Habit. 

Summary. — The critical temperature for opening flower buds varies 
greatly with their stage of development and somewhat with species and 
variety. Some of the fully expanded flowers of many fruit varieties 
will withstand an apparent temperature of 25°F. without injury, though 
some will be killed at or above this point. Unopened flower buds are 
considerably more frost resistant. Plants in a vigorous condition are 
apparently no more resistant to frost, but they possess greater recupera- 
tive ability. Often trees losing a considerable percentage of their blos- 
soms from frost still have enough good buds to bear a full crop. In 
many cases danger from frost can be avoided to a great extent by the 
selection of late blossoming varieties. Relatively greater immunity from 
frost danger can be secured in this way with those fruits and in those 
sections showing a considerable range in blossoming. The blossom- 
ing season of many fruits may be slightly retarded by certain cultural 
practices, but, except in the case of fruits like the strawberry that can 
be entirely covered, such methods of frost protection are of secondary 
importance. In new sections the probable blossoming dates of certain 
varieties of fruit may be foretold with considerable accuracy by com- 
parison with the blossoming season of native plants. The probability 
of frost occurring on any particular night can be foretold fairly accurately 
by the middle of the preceding afternoon. Several methods are employed, 



382 FUNDAMENTALS OF FRUIT PRODUCTION 

some of them being more reliable in certain districts than others. The pre- 
dictions for regular Weather Bureau "key" stations, corrected to apply to 
local conditions are of greatest general use. Several distinct methods of 
preventing frost have been used in fruit growing sections. The use of 
smoke screens is of little value in checking the radiation of heat at night. 
Orchard heating is practicable under certain conditions. However, only a 
limited protection is afforded by orchard heaters, the exact amount de- 
pending on the height of the " ceiling layer" of the air, on the number and 
kind of heaters and on the amount of wind. A protection of 4 or 5°F. on 
typical frosty nights is all that can be expected under average conditions. 
Before the installation of orchard heating equipment is warranted there 
should be reasonable assurance that growing conditions during the average 
season and the average margin of profit warrant it. Frost occurring 
after the time of fruit setting may occasionally arrest the further develop- 
ment of seeds and still permit the fleshy tissues to develop and mature, 
giving rise to fruits abnormal in size and shape. It may also cause the 
appearance of "frost rings" or bands of russet around the apical end of 
the fruit. It occasionally leads to certain other pathological conditions 
in fruit or foliage. 

Suggested Collateral Reading 

Schimper, A. F. W. Plant Geography upon a Physiological Basis. Pp. 35-51; 

241-259. Oxford, 1903. 
Chandler, W. H. Hardiness of Peach Buds, Blossoms and Young Fruit as Influenced 

by the Care of the Orchard. Mo. Agr. Exp. Sta. Cir. 31. 1908. 
Emerson, R. A. Cover Crops for Young Orchards. Nebr. Agr. Exp. Sta. Bui. 92. 

1903. 
Gladwin, F. E. Winter Injury in Grapes. N. Y. Agr. Exp. Sta. Bui. 433. 1917. 
Harvey, R. B. Hardening Processes in Plants. Jour. Agr. Res. 15: 2, 1918. 
Hooker, H. D., Jr. Pentosan Content in Relation to Winter Hardiness. Proc. Am. 

Soc. Hort. Sci. 17: 204-207. 1920. 
Macoun, W. T. Overcoming Winter Injury. Proc. Am. Soc. Hort. Sci. Pp. 15-27. 

1908-9. 
Rosa, J. T., Jr. The Hardening Process in Vegetable Plants. Mo. Agr. Exp. Sta. 

Research Bui. 48. 1921. 
Selby, A. D. Fall and Early Winter Injuries to Orchard Trees and Shrubbery by 

Freezing. Ohio Agr. Exp. Sta. Bui. 192. 1908. 
Waite, M. B. Fruit Trees Frozen in 1904. U. S. D. A., Bur. PL Ind. Bui. 51 (part 

3). 1905. 
Wiegand, K. M. The Biology of Twigs in Winter. Bot. Gaz. 41:373. 1906. 

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6. Baake, A. L. Proc. Am. Soc. Hort, Sci. 17: 279. 1920. 



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33. Ibid. P. 37. 

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37. Chandler, W. H. Mo. Agr. Exp. Sta. Cir. 31. 1908. 

38. Chandler, W. H. Mo. Agr. Exp. Sta. Res. Bui. 8. 1913. 

39. Chandler, W. H. Proc. Am. Soc. Hort. Sci. 12: 118. 1915. 

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41. Chapman, H. H. Minn. Agr. Exp. Sta. Bui. 81. 1903. 

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50. Ibid. 10: 147. 1896. 

51. Craig, J. la. Agr. Exp. Sta. Bui. 44. 1900. 

52. Crandall, C. S. Col. Agr. Exp. Sta. Bui. 41. 1898. 

53. DeCandolle, A. Geog. bot. raison. Paris, 1855. 

54. Downing, A. J. Horticulturist. 1:58. 1846. 



384 FUNDAMENTALS OF FRUIT PRODUCTION 

55. Ibid. 2: 339. 1847. 

56. Ibid. 2: 416. 1847. 

57. Duchartre, P. Compt. rend. 60: 754. 1865. 

58. Emerson, R. A. Nebr. Agr. Exp. Sta. Bui. 79. 1903. 

59. Emerson, R. A. Nebr. Agr. Exp. Sta. Bui. 92. 1906. 

60. Emerson, R. A. Nebr. Agr. Exp. Sta. Ann. Rept, 19: 101. 1906. 

61. Emerson, R. A. Correspondence, Dec. 14, 1920. 

62. Emery, S. M. Mont. Agr. Exp. Sta. Bui. 16. 1898. 

63. Emery, S. M. Mont. Agr. Exp. Sta. Bui. 24. 1899. 

64. Eustace, H. J. N. Y. Agr. Exp. Sta. Bui. 269. 1905. 

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66. Finch, V. C, and Baker, D. O. Geography of the World's Agriculture. P. 77. 

Washington, 1917. 

67. Fisher, W. R. Schlich's Manual of Forestry. 4: 505. 1907. 

68. Ibid. 4: 522. 

69. Frank, A. B. Die Krankheiten der Pflanzen. 2: 204. Breslau, 1895. 

70. Friedrich, J. Ueber den Einfluss der Witterung auf den Baumwachs. P. 155. 

Vienna, 1897. 

71. Garcia, F., and Rigney, J. W. N. Mex. Agr. Exp. Sta. Bui. 89. 1914. 

72. Ibid. Bui. 100. 1916. 

73. Gladwin, F. E. N. Y. Agr. Exp. Sta. Bui. 433. 1917. 

74. Goff, E. S. Wis. Agr. Exp. Sta. Ann. Rept, 15: 220. 1898. 

75. Ibid. 16: 283. 1899. 

76. Goff, E. S. Wis. Agr. Exp. Sta. Bui. 77. 1899. 

77. Gould, H. P. Peach Growing. P. 354. New York, 1918. 

78. Gourley, J. H. N. H. Agr. Exp. Sta. Tech. Bui. 12. 1917. 

79. Greene, L. Purdue Univ. Agr. Exp. Sta. Ann. Rept, 31: 46. 1918. 

80. Green, S. B. Minn. Agr. Exp. Sta. Bui. 32. 1893. 

81. Green, W. J., and Ballou, F. H. Ohio Agr. Exp. Sta. Bui. 157. 1904. 

82. Grossenbacher, J. G. N. Y. Agr. Exp. Sta. Tech. Bui. 23. 1912. 

83. Gunderson, A. J. 111. Agr. Exp. Sta. Bui. 218. 1919. 

84. Hammon, W. H. Cited by 71. 

85. Hansen, N. E. S. D. Agr. Exp. Sta. Bui. 50. 1897. 

86. Ibid. Bui. 65. 1899. 

87. Harvey, R. B. J. Agr. Res. 15: 2. 1918. 

88. Hedrick, U. P., Booth, N. O., and Taylor, O. M. N. Y. Agr. Exp. Sta. Bui. 275. 

1906. 

89. Hedrick, U. P. Hort. Soc. of N. Y. Mem. 2: 119. 1907. 

90. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 299. 1908. 

91. Hedrick, U. P. Plums of New York. P. 103. Albany, 1911. 

92. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 355. 1912. 

93. Herrick, R. S., and Bennett, E. R. Col. Agr. Exp. Sta. Bui. 171. 1910. 

94. Hooker, H. D., Jr. Proc. Am. Soc. Hort. Sci. 17: 204-207. 1920. 

95. Hopkins, A. D. U.S.D.A., Mo. Weather Rev. Sup. 9. 1918. 

96. Howard, A., and Howard, G. L. C. Sci. Rept. Agr. Inst, Pusa. 48. 1916-1917. 

97. Humphreys, W. J. U.S.D.A, Mo. Weather Rev. 42: 562. 1914. 

98. Jehle, R. A. Cornell Univ. Agr. Exp. Sta. Cir. 26. 1914. 

99. Johnston, E. S. Am. J. Bot. 6: 373-379. 1919. 

100. Jones, C. H., Edson, A. W., and Morse, W. J. Vt, Agr. Exp. Sta. Bui. 103. 

1903. 

101. Kimball, H. K., and Young, F. D. U.S.D.A., Mo. Weather Rev. 48: 461. 

1920. 

102. King, F. H. Wis. Agr. Exp. Sta. Ann. Rept. 13: 207. 1896. 



TEMPERATURE RELATIONS 385 

103. Lazenby, W. R. Proc. Am. Pom. Soc. P. 54. 1885. 

104. Lindley, J. The Theory and Practice of Horticulture. P. 150. London, 1855. 

105. Ibid. P. 155. 

106. Linsser, C. Cited by Bailey, L. H. Survival of the Unlike. P. 292. New 

York, 1901. 

107. Lippincott, J. B. U.S.D.A., Ann. Rept. P. 200. 1862. 

108. Livingston, B. E. Physiol. Res. 1:8. 1916. 

109. Livingston, B. E., and Livingston, G. J. Bot. Gaz. 56: 5. 1913. 

110. Lloyd, F. E. Plant World. 20: 121. 1917. 

111. Loomis, E. Treatise on Meteorology. P. 91. New York, 1892. 

112. Ibid. P. 93. 

113. MacDougal, D. T. Hydration and Growth. Cam. Inst. Wash. Publ. 297. 

P. 167. 1920. 

114. Macoun, W. T. Rept. Cent. (Can.) Exp. Farms. 12: 99. 1899. 

115. Ibid. 13: 73. 1900. 

116. Ibid. 13: 92. 1900. 

117. Macoun, W. T. Cent. (Can.) Exp. Farms Bui. 38. 1901. 

118. Macoun, W. T. Proc. Am. Soc. Hort. Sci. 3: 7. 1906. 

119. Macoun, W. T. Cent. (Can.) Exp. Farms Bui. 38. 2d ed. 1907. 

120. Macoun, W. T. Proc. Am. Soc. Hort. Sci. 6: 15. 1909. 

121. Macoun, W. T. Trans. Mass. Hort. Soc. Pt. 1. P. 39. 1916. 

122. Marvin, C. F. U.S.D.A., Mo. Weather Rev. 42: 583. 1914. 

123. Mason, S. C. U.S.D.A., Bur. PI. Ind. Bui. 192. 1911. 

124. Maynard, S. T. Agriculture of Massachusetts. P. 348. Boston, 1884. 

125. Maynard, S. T. Mass. Agr. Exp. Sta. Bills. 10. 1890; 15. 1891; 21. 1893. 

126. McAdie, G. U.S.D.A, Mo. Weather Rev. 40: 282. 1912. 

127. Ibid. 40: 618. 

128. McCall, F. E. Amer. Fruit Grower. 39: 7. July, 1920. 

129. McLean, F. T. Physiol. Res. 2: 129. 1917. 

130. Mell, P. H. Ala. Agr. Exp. Sta. Bui. 8. 1890. 

131. Mer, E. Compt. rend. 114: 242. 1892. 

132. Ibid. 124: 1111. 1897. 

133. Mikesell, T. U.S.D.A., Mo. Weather Rev. Sup. 2. 1915. 

134. Milham, W. I. U.S.D.A., Mo. Weather Rev. 36: 250. 1908. 

135. Mix, A. J. Cornell Univ. Agr. Exp. Sta. Bui. 382. 1916. 

136. Moore, W. L. Descriptive Meteorology. P. 82. New York, 1911. 

137. Mosier, J. G. 111. Agr. Exp. Sta. Bui. 208. 1918. 

138. Muller-Thurgau, H. Landw. Jahrb. 45: 453. 1886. 

139. Munson, W. M. Me. Agr. Exp. Sta. Ann. Rept. 7: 96. 1893. 

140. N. Y. Agr. Exp. Sta. Ann. Rept. 37: 468. 1919. 

141. O'Gara, P. J. U.S.D.A., Farmers' Bui. 401. 1910. 

142. Oskamp, J. Proc. Am. Soc. Hort. Sci. 14: 118. 1917. 

143. Paddock, W., and Whipple, O. B. Fruit Growing in Arid Regions. P. 325. 

New York, 1911. 

144. Ibid. P. 326. 

145. Ibid. P. 327. 

146. Ibid. P. 353. 

147. Pantanelli, E. Atti. accad. Lincei. 27(1): 126-130; 148-153. 1918. 

148. Pa. Agr. Exp. Sta. Ann. Repts. 1892, 1893, 1894, 1895, 1896. 

149. Petit, A. Rev. hort. 13(N.S.): 206. 1913. 

150. Pfeffer, W. Physiology of Plants. Transl. by Ewart. 2: 236. Oxford, 1903. 

151. Ibid. 2: 237. 

152. Ibid. 2: 246. 

25 



386 FUNDAMENTALS OF FRUIT PRODUCTION 

153. Philips, H. A. Thesis. Cornell Univ. 1920. 

154. Porter, E. D. Minn. Agr. Exp. Sta. Bui. 7. 1889. 

155. Price, H. L. Va. Agr. Exp. Sta. Ann. Rept. P. 206. 1909-1910. 

156. Prillieux, E. Compt. rend. 74: 1344. 1872. 

157. Quaintance, A. L. Ga. Agr. Exp. Sta. Ann. Rept. 11: 123. 1899. 

158. Ragan, W. H. U.S.D.A., Div. Pom. Bui. 8. 1899. 

159. Reed, W. G. Proc. 2d Pan-Amer. Sci. Cong. P. 625. 1917. 

160. Reed, W. G., and Tolley, H. R. U.S.D.A., Mo. Weather Rev. 44: 354. 

1916. 

161. Roberts, R. H. Proc. Am. Soc. Hort. Sci. 14: 105. 1917. 

162. Rosa, J. T. Jr. Proc. Am. Soc. Hort. Sci. 16: 190. 1919. 

163. Ibid. 17: 207-210. 1920. 

164. Rosa, J. T. Jr. Mo. Agr. Exp. Sta. Res. Bui. 48. 1921. 

165. Sandsten, E. P. Wis. Agr. Exp. Sta. Ann. Rept. 21: 258. 1904. 

166. Sandsten, E. P. Wis. Agr. Exp. Sta. Bui. 137. 1906. 

167. Sandsten, E. P. Wis. Agr. Exp. Sta. Res. Bui. 4. 1910. 

168. Schimper, A. F. W. Plant Geography upon a Physiological Basis. P. 34. 

Oxford, 1903. 

169. Ibid. P. 37. 

170. Ibid. P. 45. 

171. Ibid. P. 47. 

172. Schneider, Numa. Rev. hort. 11(N.S.): 21. 1911. 

173. Schiibler, G. Poggendorf's Annal. Phys. u. Chem. 10: 581. 1827. 

174. Schuster, C. E. Ore. Agr. Exp. Sta. Bien. Crop Pest and Hort. Rept. 3: 44. 

1920. 

175. Seeley, D. A. U.S.D.A., Mo. Weather Rev. 36: 259. 1908. 

176. Ibid. 45: 354. 1917. 

177. Selby, A. D. Ohio Agr. Exp. Sta. Bui. 192. 1908. 

178. Selvig, C. G. Rept. Exp. Farm, Crookston, Minn. 1917-18. 

179. Shaw, J. K. Mass. Agr. Exp. Sta. Ann. Rept. 23: 177. 1911. 

180. Shutt, F. T. Trans. Roy. Soc. Can. (Ser. 2.) 9(4): 149. 1903. 

181. Smith, A. M. Ann. Roy. Bot. Gar. Peradeniya. (Abs. in Bot. Gaz. 44: 6. 

1917.) 

182. Smith, J. W. U.S.D.A, Mo. Weather Rev. Sup. 16. 1920. 

183. Sorauer, P. Schutz der Obstbaume gegen Krankheiten. P. 42. Stuttgart, 

1900. 

184. Ibid. P. 46. 

185. Squires, R. W. Minn. Bot. Studies. 1 : 452. 1894-8. 

186. Stevens, N. E. Am. J. Bot. 4: 1. 1917. 

187. Ibid. 4: 112. 

188. Stockman, W. B. U.S.D.A., Mo. Weather Rev. 32: 125. 1904. 

189. Strausbaugh, P. D. Bot. Gaz. 71: 337. 1921. 

190. Swezey, G. D. Nebr. Agr. Exp. Sta. Ann. Rept. 16: 95. 1903. 

191. Swingle, W. T. U.S.D.A., Bur. PI. Ind. Bui. 53. 1904. 

192. Taft, L. R. Mich. Agr. Exp. Sta. Sp. Bui. 11. 1898. 

193. Ibid. Sp. Bui. 40. 1907. 

194. Ibid. Sp. Bui. 46. 1908. 

195. Taft, L. R., and Lyon, T. T. Mich. Agr. Exp. Sta. Bui. 169. 1899. 

196. Tufts, W. P. Correspondence, 1921. 

197. Von Mohl, C. Bot. Ztg. 6: 6. 1848 

198. Waite, M. B. U.S.D.A., Bur. PI. Ind. Bui. 51. 1905. 

199. Waldron, C. B. N. D. Agr. Exp. Sta. Bui. 25. 1896. 

200. Ibid. Bui. 49. 1901. 



TEMPERATURE RELATIONS 387 

201. Ward, H. W. The Book of the Peach. P. 27. London, 1903. 

202. Waugh, F. A. Vt. Agr. Exp. Sta. Bui. 62. 1898. 

203. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 11: 270. 1898. 

204. Ibid. 11: 273. 

205. Waugh, F. A. Vt. Agr. Exp. Sta. Bui. 74. 1899. 

206. Webber, H. J. et al. Cal. Agr. Exp. Sta. Bui. 304. 1919. 

207. West, F. L., and Edlefsen, N. E. Utah Agr. Exp. Sta. Bui. 151. 1917. 

208. West, F. L., and Edlefsen, N. E. J. Agr. Res. 20: 8. 1921. 

209. Whipple, O. B. Mont. Agr. Exp. Sta. Bui. 91. 1912. 

210. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 38. 1897 

211. Ibid. Bui. 49. 1900. 

212. Whitten, J. C. Mo. Agr. Exp. Sta. Res. Bui. 33. 1919. 

213. Wiegand, K. M. Bot. Gaz. 41:373. 1906. 

214. Wiegand, K. M. Plant World. 9: 2. 1906. 

215. Wilcox, E. V. Mont. Agr. Exp. Sta. Bui. 22. 1899. 

216. Wilson, W. M. Standard Cyclopedia of Horticulture. 3: 1282. 1915. 

217. Winkler, H. Jahrb. f. Wiss. Bot. 52: 467. 1913. 

218. Young, F. D. U.S.D.A., Farmers' Bui. 1096. 1920. 

219. Young, F. D. U.S.D.A., Mo. Weather Rev. 48: 463. 1920. 



SECTION IV 
PRUNING 

Fruit production by the trees, shrubs and vines that yield edible 
fruits is dependent on (1) the possession of the mechanism or machinery 
for fruit production that is characteristic of the species or variety in 
question and (2) its proper and more or less efficient functioning. Thus 
it is characteristic of most varieties of the brambles to bear fruit clusters 
terminally on short shoots developing from lateral buds on year-old 
canes. If the plant is so handled as to prevent or reduce the formation 
of lateral shoots of this type, fruiting is correspondingly limited. It is 
characteristic of certain varieties of the walnut to bear terminally only 
on short shoots developing from terminal buds on the growth of the previ- 
ous season. Obviously then the production and preservation of terminal 
buds is a prerequisite to fruit production in those varieties. The peach 
bears fruit on shoots of the past season but only at nodes from which no 
lateral branches arise. 

However, some of the lateral buds on last year's raspberry and black- 
berry canes do not produce fruiting shoots; some of the shoots from ter- 
minal buds of the walnut are barren and many nodes on the unbranched 
primary peach shoot do not have fruit buds. The framework, the 
machinery, for fruit bud formation is apparently there, but no fruit buds 
are formed. The mechanism does not function in the way it is desired. 
This functioning or non-functioning of the fruiting machinery is to be 
regarded as a definite response to varying conditions within the tree — 
primarily conditions of nutrition, which in turn may be influenced by 
age, vigor, food supply, temperature, humidity and many other factors. 

In some cases production is limited by the amount of fruiting machin- 
ery, or, as the grower would say, the amount of bearing surface. In 
others the limiting factor to production is the irregular, imperfect or 
inefficient functioning of the fruiting mechanism. For the grower the 
ideal condition is to have the plant well equipped with fruit producing 
machinery and to have that machinery working efficiently. One or two 
further parallels may be drawn at this point between the living plant and 
the hypothetical manufacturing establishment with which it has been 
compared. Good equipment with fruit producing machinery does not 
mean the maximum amount that can be crowded into the available room 
any more than an amount plainly inadequate for the establishment. Too 
much fruiting wood unduly taxes the tree for its maintenance. On the 

388 



PRUNING 389 

other hand maximum production cannot be expected from a half -equipped 
plant. An efficiently working machine is not one that is carrying an over- 
load any more than it is one carrying half or a third of a load. Regular, 
steady, annual production of large but not maximum amounts is desirable. 
Perhaps in certain species the problem of securing heavy and regular fruit 
production is somewhat simpler than has been indicated. In the jaboticaba 
whose blossoms and fruits come out indiscriminately anywhere on the bark, 
from the crown or even exposed roots to the tips of the youngest branches, the 
question of developing a special fruit producing mechanism never arises. The 
plant cannot grow without developing its fruit machinery and it is only the 
proper functioning of this bark that is a limiting factor to production. Certain 
other tropical and subtropical fruits present other apparent exceptions to the 
general statements that have been made, but they need not be given serious con- 
sideration here, for they do not alter materially the general principles involved 
or their application in deciduous fruit production. 

Therefore it is desirable to determine as nearly as possible the exact 
nature of the fruiting habits of the different species and the methods by 
which they can be modified and controlled. What is the fruiting mechan- 
ism of the various fruits? What constitutes an adequate equipment for 
plants of different sizes or ages? How can the amount best be increased 
or limited? How does it usually function under varying conditions? 
What methods can be employed to make it work at full efficiency, carry a 
full load, year after year? How long does the machinery last? What are 
the best means of getting rid of useless or inefficient machinery and of 
securing new equipment? When is it best to attempt to repair and speed 
up equipment that is working poorly and when is it best to discard it and 
obtain new? The answers to these and many other related questions are 
of first importance to the grower, for profitable production depends on 
them to no small degree. 



CHAPTER XXI 
GROWING AND FRUITING HABITS 

Left to themselves the plants of each species, or even of each variety 
show more or less distinctive growing and fruiting characteristics. The 
former are partly under the control of the grower, so that it is possible 
for him to make plants of quite different growing habits assume a nearly 
uniform shape in the orchard or to train two of the same kind so that they 
appear very unlike. His control over bearing habits is less complete 
though much can be done to modify them in- certain directions. Both are 
influenced directly or indirectly by nearly every cultural practice. Prun- 
ing, however, using that term in its broader sense, is the most direct and 
most important of these practices. 

Some growers prune their trees; some do not. Others prune some of 
their fruit trees, but leave other kinds unpruned. The trees or plants of 
certain species are quite generally given some kind of pruning treatment; 
those of certain other species are almost as generally let alone. In some 
orchards pruning is a regular annual operation; in others it is done bienni- 
ally or at long irregular intervals. There is no horticultural practice con- 
cerning which there is a greater diversity of opinion or in the application 
of which there is a greater diversity of procedure. If the average grower 
is asked why he prunes or why he does not his answer is likely to be that he 
believes it is good for the tree or that it is not good for it. Seldom does he 
give specific objects that he has in mind or that he believes may be accom- 
plished by means of pruning. If specific objects are mentioned they are 
likely to be among the following: (1) to open the tree so that the fruit 
will color more satisfactorily, (2) to train it to some desired form, (3) to 
remove dead or diseased limbs, (4) to remove water sprouts, (5) to thin 
the fruit. 

All of these are accomplished by pruning if the work is done properly; 
nevertheless they are not its primary objects. Fundamentally, pruning, 
in common with other cultural practices, should be directed to encourage 
the production of larger quantities of fruit, the production of fruit of 
better grade, or to lower the cost of production ; its value, like that of 
any other orchard operation, may be determined by the extent to which 
it contributes in any one or more of these three directions. 

Pruning may be considered from many points of view and subdivided 
in many ways. In the following discussion it is considered briefly as a 

390 



GROWING AND FRUITING HABITS 391 

means of modifying shape and in more detail as it influences development, 
location and functioning of the fruiting machinery of the tree. 

PRUNING FOR FORM— TRAINING 

There is frequent failure to distinguish clearly between pruning and 
training. The two practices are often regarded as one and the same or 
at least as inseparable. Training concerns form primarily; pruning 
affects function primarily. Training determines the general character 
and even the details of the plant's outline and of its branching and frame- 
work; pruning is meant to assist more in determining what the tree 
does in respect to fruiting. Training may be illustrated by reference 
to what may be done easily with the grape. Without cutting off or 
cutting back a single cane, it is possible to train a vine on a one-wire 
trellis, a two-wire trellis, a three-wire vertical trellis, a three-wire hori- 
zontal trellis, an arbor, or in any one of a dozen other ways. The 
training simply gives the vine its form and has comparatively little to 
do with the number or size of the bunches of fruit it produces. Similarly, 
fruit trees are made to assume one form or another — for example, high- 
headed or low-headed, open-centered or closed-centered, flat-topped or 
pyramidal — and production is influenced comparatively little by these 
shapes. It is true that the pruning saw and shears are generally used in 
forcing the trees into the one shape or the other, and hence, perhaps the 
operation should be spoken of as "pruning for form." Nevertheless 
the operation affects form principally and consequently is here discussed 
under the heading of training, even though strictly speaking the use of 
that term should be limited to such changes in form as are effected with- 
out the removal of parts. If parts are removed at such a time and in 
such a way as to modify materially the functioning of the whole tree or of 
some of its parts, even though its general shape is left unchanged, the 
operation should be considered pruning. Many times both shape and 
function are modified by a single operation, which then is to be regarded 
as both pruning and training; often, however, it is chiefly one feature of 
the tree's growth that is influenced. 

General Objects. — In general, training has little direct effect on 
the amount of fruit borne. Some of the pruning practices that accom- 
pany certain methods of training may affect yields profoundly, but the 
training in itself is of only secondary importance in this connection. On 
the other hand training may be a factor in determining grade, or what 
is frequently referred to as " quality. " Its influence on grade is produced 
largely through making it difficult or easy to spray thoroughly and 
consequently in aiding or hindering the control of insects and diseases. 
Standard control measures for certain pests may lose half of their effi- 
ciency if the plants have been untrained or poorly trained. This influ- 
ence is distinct from and additional to the direct control of certain pests 



392 FUNDAMENTALS OF FRUIT PRODUCTION 

by cutting out and destroying infected parts. In certain fruits the 
shape and openness of the tree is important in influencing the colora- 
tion. Training is important also in reducing certain production costs. 
Tillage and other soil treatments, spraying, thinning, propping, trellising 
and harvesting all may be greatly facilitated by proper training. 

In a general way training should tend so to distribute the fruiting 
wood and the fruit that all orchard or vineyard operations may be con- 
ducted with greatest facility and lowest cost. It should eliminate or 
minimize the necessity and cost of trellising, propping, or artificially 
supporting the plant and its fruit. It should provide the leaves and 
developing fruits with as nearly as possible optimum conditions for 
coloration without danger from sunscald and, wherever feasible, it 
should aim to provide those conditions least favorable for the work of 
injurious insects and diseases. In view of all these possible effects of 
training and of the widely varying conditions under which plants of even 
the same variety are grown, it is evident that the best method of training 
a plant in one situation may be quite distinct from what is best in 
another and it often happens that two fruits or two varieties of the same 
fruit should be trained differently when grown in the same environment. 

Since the training of trees presents certain problems quite distinct 
from those of pruning it seems desirable to consider them separately 
from their possible influence on function. 

Details in Training. — A comparatively large part of the training 
that trees are to receive should be given during the first few years of 
their growth. It is during this period that they are building their frame- 
work and taking on the general form that the grower has decided shall 
be theirs during the rest of their lives. During later years efforts are 
directed mainly to preserve the form already given the tree and attention 
is given to its pruning as distinguished from training. 

Height of Head. — By height of head is meant the distance from the 
ground at which the main or scaffold limbs branch from the trunk. 
Trees in which the scaffold limbs come out within 2% or 3 feet from the 
ground are spoken of as low-headed; those in which they come out from 
the trunk 4 feet or more from the ground are high-headed. The height 
of head generally is established at the time of setting by the distance 
from the ground at which the top is cut off though it is possible to raise 
the head or sometimes to lower it by later treatment. In the older 
orchards high-headed trees are the rule. It was thought that high- 
heading facilitated cultivation and other orchard operations and perhaps 
was better for the tree. More recent tendencies have been in the 
direction of lower heads. If properly handled it is no more difficult to 
cultivate around and under such trees and pruning, spraying, thinning 
and picking are greatly facilitated. Furthermore, low-headed trees are 
less subject to sunscald and suffer less from high winds. 



GROWING AND FRUITING HABITS 393 

Number of Scaffold Limbs. — The number of scaffold limbs found in 
orchard trees varies from 2 to 15 or 20. Neither extreme is desirable. 
If there are only two or three main scaffold limbs they are almost certain 
to form crotches that are likely to split and allow one or both parts to 
break down. A large percentage of the injury resulting from trees break- 
ing when heavily loaded with fruit or when subjected to severe winds 
is due indirectly to sharp crotches that could have been avoided by the 
use of more and better spaced scaffold limbs. Should one limb of a 
group of three split down, a third of the tree is gone; should one of eight 
be lost, most of the tree still remains and the injury, which is much less 
likely to happen, is more readily repaired. On the other hand too many 
scaffold limbs, as 10 to 12, give rise to thick, brushy tops that make 
work in them difficult. A moderate number, five to eight, makes a 
tree that is mechanically strong and at the same time open enough to 
facilitate necessary orchard operations. 

Distribution of Scaffold Limbs. — Of still greater importance than the 
number of scaffold limbs is their distribution. When they come out from 
the trunk at points close together, as for instance, when the upper one of 
five is only 8 or 10 inches above the lowest they form bad crotches much 
sooner than if they are distributed over a longer distance on the trunk. 
When they are distributed over 1% or 2 feet of the trunk each limb has 
a chance to make more or less " shoulder;" weak crotches with subsequent 
splitting are avoided. It may require a little attention to select and 
develop scaffold limbs that are separated well from one another, on 
account of the tendencjr of the tree to make its most vigorous growth 
from buds near the end of the trunk or near the extremities of its branches 
but it is well worth while. Furthermore, it should be remembered that 
the distribution of these limbs is determined once and for all by the first 
two or three prunings and no amount of later work will entirely correct 
a mistake made then. If a tree is headed at a height of 33 to 36 inches 
it is possible to have a good number of well-distributed limbs and at the 
same time have a low-headed tree. One of the main advantages of the 
"modified leader" type of training is the opportunity for a wide spacing 
of the scaffold limbs. 

Open and Closed-centered Trees.' — There has been much discussion over 
the relative merits of open-centered or vase-shaped and close-centered 
or leader trees. Both forms have their advocates. Both are extensively 
used and both are successful — good evidence that the exact form in which 
trees are trained is a matter of secondary importance from the standpoint 
of production. Theoretically at least, the open-centered method of 
training admits more sunlight and thus enables the fruit to attain a 
higher color than is possible in the closed-centered tree, though in reality 
the tree that is started with the open center is often allowed to become 
more thick-topped than many "leader" trees. Obviously, this is a 



394 FUNDAMENTALS OF FRUIT PRODUCTION 

matter that can be of no real importance in fruits where coloration does 
not depend on the light reaching the fruit itself . From the very nature of 
the case the central-leader type of tree forms more scaffold limbs than the 
open-centered tree and consequently it is less likely to split at the crotches. 
It is often more bushy-topped but this condition is not necessary. 

It has become a generally accepted practice to train certain fruits in 
certain styles. For instance, peaches are almost always grown in the 
vase form and pears are trained with a central leader. In some cases 
whole sections use a certain style for practically all their tree fruits. To 
what extent these practices are based on careful comparisons of different 
methods of training for the fruit or the locality in question and to what 
extent they are followed simply because the custom has become estab- 
lished is often difficult to say. A careful study of training methods might 
lead in many cases to some change that would be of considerable com- 
mercial importance to the particular district or for the particular variety. 

The general method of procedure in training a tree to the central- 
leader type is each year to prune back the central and upper shoot or 
leader less severely than the lateral shoots or limbs surrounding it. If an 
open-centered tree is desired the opposite method should be followed. 
It is a mistake in attempting to train a tree to the open-centered type 
to cut out entirely the interior and central limbs. This merely provokes 
the production of water sprouts to take their place and more cutting out 
must be done. By cutting back the interior and upper shoots and limbs 
more severely than the outer, the former are subordinated and the latter 
are made the dominant limbs in the tree. In other words, it is easier 
and better to grow an open-centered tree with a comparatively open 
center- — with only a few, small, subordinate, fruiting branches in the 
interior — than one with a completely open or hollow center. 

A different type of training that is coming into favor is known as 
the "modified leader." As the name suggests, it is intermediate between 
the open-centered and the leader tree. It is developed by training to the 
leader type for the first 4 or 5 years and from then on as an open-centered 
tree. This results in a tree with a central leader extending some 3 to 5 
feet above the point where it was originally headed and then an open 
center above that. It possesses practically all the advantages of the two 
other types and few or none of their disadvantages. 

Trees of Different Shape. — Less attention need be devoted to the 
general shape of the tree than to certain other features of its training. 
Nevertheless, there are occasional arguments for flat-topped or round- 
topped trees or other forms. In general, little emphasis should be placed 
on these particular shapes. It is not a bad plan to allow the tree con- 
siderable freedom in assuming the general shape that is natural. Training 
for form should be limited to correcting minor defects rather than altering 
profoundly the shape. 



GROWING AND FRUITING HABITS 395 

Lowering the Tops of Trees. — In the course of time the trees of many 
species become so tall that the added cost of gathering the fruit from the 
topmost branches reduces the margin of profit to the vanishing point. 
Furthermore the higher branches shade the lower and reduce their effi- 
ciency as fruit producers. The increased difficulty in controlling insects 
and diseases in the tops of very tall trees, even with the aid of the best of 
the present power spraying outfits, makes those portions of doubtful 
value to the grower even though it should be possible to harvest the 
fruit economically. One investigator sets 25 feet as about the limit 
in height for profitable apple production 12 and with the smaller spraying 
outfits the limit is probably well below that figure. The problem of 
controlling the height of trees and keeping their lower branches actively 
producing a good grade of fruit is thus very real. 

Many growers wait until the trees get much too tall for profit and then 
"dehorn;" that is, they cut back the limbs severely, leaving large stubs 
that promptly send out an abundance of strong vigorous watersprouts. 
Eventually new fruiting wood is developed from this new growth, but in 
the meantime crowding is likely to force this new growth up, so that by 
the time the top has been bearing a few years it is too high again and 
another dehorning becomes necessary. 

A much better method of lowering the tops of tall trees is to cut back 
into 2-, 3-, or 4-year-old wood, always to a lateral branch. The more 
nearly horizontal this side limb, the better. By thus cutting to a lateral 
the flow of sap is utilized in a somewhat increased growth and few or no 
watersprouts develop. A year or two later this lateral can be cut back 
to one of its side branches, or perhaps the whole structure can be removed, 
the cut being to a still lower side limb on the main branch that in the mean- 
time has been strengthened by the heading back of the season before. 

This, it will be recognized, is a procedure aiming constantly to keep 
the tree within bounds rather than permitting it first to become far too 
tall and then greatly reducing its height. To be most successful it 
should begin when the tree reaches about the desired height and from 
then on it should constitute a part of the regular annual treatment that 
the tree receives. It will not be necessary to lower every part or limb 
of every tree each year; only the tallest, those getting too high, need be 
cut back. This practice not only results in the production of fewer 
watersprouts but it keeps the lower part of the tree in a better producing 
condition than is possible with occasional dehorning. It is a heading 
back in name mainly- — really resulting in more thinning than cutting 
back — and is followed by the kind of a response that attends thinning 
out. 

Eliminating and Subordinating Limbs. — It has just been stated that 
in the training of open-centered trees it is usually better to suppress or 
subordinate the interior limbs than to attempt their total elimination. 



396 FUNDAMENTALS OF FRUIT PRODUCTION 

This last can be done by cutting them out and then repeatedly removing 
watersprouts that take their place, but this involves much labor. If 
they are subordinated the water sprout problem is largely eliminated 
and they may serve as fruit-producing branches for many years. In 
apples, pears and other spur-bearing fruits, their retention may also aid 
materially in bringing the trees into bearing earlier, because if properly 
handled they develop fruit spurs and fruit buds freely at a period when 
heavy pruning back for proper form may prevent to a great extent 
formation of spurs on the more permanent framework of the tree. Often 
one of the best ways to subordinate and make fruiting branches from 
these interior limbs is to let them remain with no heading back at the 
beginning of their second season. They then produce short vegetative 
growths from their terminal buds, with few or no lateral shoots but with 
many lateral spurs. After their second season's growth they are headed 
back into 2-year-old wood. Treated in this way they make but little 
further shoot growth and little difficulty is experienced in keeping them 
as subordinate fruit-bearing limbs. 

Preventing the Formation of Crotches. — It is a principle of rather gen- 
eral application that the unequal cutting back of two parts in the same 
tree or plant tends to subordinate that part pruned more severely and 
to give the advantage to the other. Equal cutting of two shoots or 
limbs of about the same length results in their equal subsequent develop- 
ment into a fork or crotch that is a point of weakness in the framework of 
the tree. Crotches can be largely avoided and the framework corre- 
spondingly strengthened by pruning with the idea of making one of two 
equal branches a leader and the other a lateral subordinate to it. 

BEARING HABITS 

There is reason to believe that with proper nutritive conditions in the 
plant, particularly with an accumulation of certain carbohydrates, any 
partly developed bud may undergo differentiation, form flower parts 
and develop as a fruit bud. This assumes that other limiting factors, 
such as moisture and temperature, are favorable. It is conceivable that 
in the developing buds of some plants a stage is finally reached when 
such a differentiation cannot take place except by the unfolding of the 
bud into a leafy structure and the subsequent formation of the fruit bud 
at a new growing point. In general, though, every bud is to be regarded 
as a potential flower bud. In every kind of plant, however, most of the 
flower buds are formed in certain definite positions, probably because it 
is only in those positions that nutritive and other conditions favorable 
for flower bud formation ordinarily occur. It is therefore possible to 
speak of the bearing or fruiting habit of a plant, though the use of this 
term does not mean that other types of bearing, other fruiting habits, 
may not be found on the same plant under unusual conditions. Not 



GROWING AND FRUITING HABITS 397 

infrequently the crop borne from flowers appearing in such an unusual 
place exceeds that produced by those considered characteristic. For 
instance, the nectarine would be classed generally as a tree bearing its 
fruit buds laterally on shoots, but the Stanwick variety is as typical a 
spur bearer as the Montmorency cherry. 

Since all buds are to be regarded as potential flower buds, flowers or 
inflorescences and hence fruits, may be borne wherever buds are borne — 
usually (1) terminally on long or short growths, or (2) laterally in the 
axils of the current or past season's leaves and now and then (3) adven- 
titiously from any point on the exposed bark of limbs, trunks or roots. 
As a rule the position of the flower or inflorescence on the shoot relative 
to the growth of the current season is characteristic of the species or 
variety and is subject to but little change. The inflorescences of the 
raspberry and blackberry are always terminal to the growth of the current 
season and the flowers or inflorescences of the persimmon are always 
lateral. Flower-bearing shoots may arise from either terminal or lateral 
buds on either long or short growths (spurs), or they may arise from 
adventitious buds. There is often considerable variation within the 
species, variety, or even individual plant in this respect. 

Relation of Growth Habits to Position of Fruit Buds. — Within limits 
certain habits of growth are necessitated by or at least are associated with, 
particular fruiting habits. In general, plants with terminal fruit buds 
have a somewhat restricted habit of growth. Terminal bearing tends to 
promote greater compactness of tree or plant than bearing from lateral 
fruit buds, because it forces the development of laterals from below, 
rather than beyond, the flowers or flower clusters. Plants whose fruit 
buds are borne either terminally (apple) or laterally (sweet cherry) on 
short growths or spurs are generally more compact than those like the 
peach or grape whose fruit buds are borne on long shoots and the problem 
of preventing their bearing areas from getting too far away from the 
trunk or head of the plant is less serious. If fruit buds are borne later- 
ally on long shoots there may be a distinct difference in the general man- 
ner of growth, depending on whether they are found principally on the 
basal, median or distal portion and the grower will employ a "short," 
"medium" or "long" pruning system, as the case may be. 

Different Kinds of Flower-bearing Shoots. — Regardless of the location 
of the fruit bud — that is, whether terminal or lateral — when it unfolds it 
may give rise to any one of three distinct types of flower-bearing struc- 
tures: (1) it may contain flower parts only and develop a single flower 
(as in the peach) or a flower cluster (as in the cherry) without leaves, (2) 
it may be a mixed bud and develop a short or long leafy shoot terminating 
in an inflorescence (as in the apple), (3) it may be mixed and develop a 
short or long leafy shoot bearing flowers or flower clusters in some of its 
leaf axils (as in the persimmon). 



398 FUNDAMENTALS OF FRUIT PRODUCTION 

Classification of' Fruits According to Fruiting Habits 





Fruit buds terminal 


Fruit buds lateral 




I 


IV 


Flower bud containing 


Loquat 


Peach 


flower parts only 


Mango 


Plum 

Apricot 

Cherry 

Almond 

Plumcot 

Currant 

Gooseberry 

Kumquat 

Northern papaw 

Walnut (staminate catkins) 

Hickory (staminate catkins) 

Pecan (staminate catkins) 




II 


V 


Flower bud mixed 


Apple (principally) 


Blackberry 


Flowering shoot with 


Pear (principally) 


Raspberry 


terminal inflorescences 


Quince 


Dewberry 




Medlar 


Grape 




Hawthorn 


Filbert 




Haw 


Blueberry 




Elder 


Cranberry (European) 




Juneberry 


Cashew nut 




Walnut (pistillate flowers) 


Brazil nut 




Hickory (pistillate flowers) 


Pond-apple (and various 




Pecan (pistillate flowers) 


other anonaceous fruits) 
Apple (occasionally) 
Pear (occasionally) 




III 


VI 


Flower bud mixed 


Guava 


Persimmon 


Flowering shoot with 


Tropical almond 


Mulberry 


lateral inflorescences 


Rose-apple (and other species 


Fig 




of Eugenia) 


Cranberry (American) 




Olive (partly) 


Chestnut 

Chinquapin 

Oak 

Beech 

Pistachio 

Star-apple 

Jujube 

Avocado 

Olive (partly) 



GROWING AND FRUITING HABITS 399 

A Classification of Plants According to Bearing Habits. — Since the 
flower bud itself is either terminal or lateral, there are six main types of 
fruiting, six distinct bearing habits, the classification being based upon 
the location of the fruit buds and the type of flower-bearing structure to 
which they give rise. These six main groups together with the more 
important of the fruits they include are shown in the accompanying 
diagram. 

There are endless variations within these main groups; certain 
species or varieties sometimes bear in one way and sometimes in another, 
or in two or more ways at the same time. 

The following discussion points out some of the peculiarities of the 
more important fruits. Several special groups also are included to bring 
together those fruits having in their bearing habits certain peculiarities 
that make it desirable to consider them separately from the main groups 
to which they might be referred. 

Group I. — Fruit buds borne terminally, containing flower parts only 
and giving rise to inflorescences without leaves. 

None of the common deciduous fruits has this bearing habit. It is best 
illustrated perhaps by the loquat and the mango (see Fig. 39). Growth is con- 
tinued by branches rising from lateral buds below the inflorescence ; some of these 
branches form terminal buds for a succeeding crop. The indications are that in 
the mango fruit bud differentiation does not take place long before the flowering 
season and sometimes two, three or even four crops of flowers are formed during 
the year, though this is not likely if there is a good set of fruit which is carried 
through to maturity. In case some accident happens to the terminal flower bud 
of the mango, some of the axillary buds may differentiate flower parts and thus 
form fruit buds. 

Group II. — Fruit buds borne terminally, unfolding to produce 
leafy shoots that terminate in flower clusters. 

This bearing habit is characteristic of most of the pome fruits and is 
found likewise in a few others of minor economic importance. 

In the apple and pear most of the terminal fruit buds are on spurs, 
(see Fig. 40) though in young vigorous trees of certain varieties many 
of the long shoots form terminal flower buds. Seldom, however, is any 
considerable percentage of the crop borne in this latter way. The fruit 
buds of these plants are mixed and invariably give rise to very short 
growths with a few short internodes, leaves of ordinary size and a lateral 
branch (sometimes two or more) arising in the axil of one of the leaves; this 
branch may bear fruit the following season, though usually fruit bud 
formation is delayed a year or more. The spur may live a great many 
years and bear repeatedly. The actual records of individual spurs 
generally show an irregularly alternate bearing habit. New spurs origi- 
nate from lateral buds on shoots of the preceding season and occasionally 
from latent or adventitious buds on the trunk or older limbs. The 



400 



FUNDAMENTALS OF FRUIT PRODUCTION 



continued bearing of the individual spurs makes for a comparatively 
compact type of tree growth. 

The juneberry or shadbush (Amelanchier) and hawthorn or azarole (Cratae- 
gus) have bearing habits practically identical with those of the apple and pear 
just described. 

Mention should be made that both the apple and pear occasionally bear 
lateral fruit buds on long shoots. Certain varieties, like Wagener, are particu- 
larly given to this habit. It is found more frequently in young vigorous trees 
than in those with a settled bearing habit. However, the fact that it may occur 
on almost any variety and that occasionally a considerable percentage of the 
crop may be borne in this way, is evidence that this habit is a response to unusual 
nutritive conditions. The special treatment that should be accorded trees 
fruiting in this manner is discussed under Pruning of the Apple and Pear. 






I 

Figs. 39-42. — Diagrams showing (from left to right) bearing habits of loquat, apple 
olive and peach. F equals fruit; B equals flower bud; L equals leaf bud. One-year-old 
wood shown by solid line, two-year-old wood by broken line. 

The bearing habit of the quince and the medlar is similar to that of the 
apple and pear, except that when the terminal (mixed) fruit bud unfolds 
it gives rise to a leafy shoot of medium length, with medium long instead 
of short internodes and the flowers are borne terminally on this shoot. 
Fruit buds for the following season's production are borne terminally on 
shoots springing from lateral buds on either flowering or non-flowering 
shoots, or from terminal buds on older shoots that the year before did not 
differentiate flower buds. These fruits consequently are not such com- 
pact growers as the apple or pear, though the shorter growth of their 
purely vegetative shoots and the greater tendency for their lateral buds to 
grow rather than remain latent may give them a very thick and brushy 
appearance. 

The haw (Viburnum), elder (Sambucus), and clove (Caryophyllus aromaticus) 
have bearing habits similar to the quince and medlar, though occasionally they 
differentiate flower buds terminally, like the apple and pear on short growths, 
which are essentially spurs. All these fruits are opposite-leaved and it fre- 
quently happens that the lateral buds in the axils of the upper leaves differenti- 
ate flower parts. This is more likely to happen if the terminal bud is injured or 
destroyed. 



GROWING AND FRUITING HABITS 401 

Group III. — Fruit buds borne terminally, unfolding to produce 
leafy shoots with flowers or flower clusters in the leaf axils. 

This might be called an incomplete terminal bearing habit, for the 
fruit itself is not borne terminally, but is lateral to the growths upon which 
it appears. However, the flower buds are terminal. The terminal buds 
of the flowering shoots may differentiate flower parts for the following 
year's production or new buds may develop from lateral leaf buds. 

None of the common deciduous fruits has this bearing habit. It is found in 
the pomegranate, the tropical almond {Terminalia catappa), the guavas (Psidium 
spp.), the olive, and in a number of the species of Eugenia. In the pomegranate, 
guava and in the Eugenias the fruit buds are formed on short shoots or spurs 
and the flowers and fruits in the axils of the outermost leaves. In the olive the 
inflorescences are generally found in the axils of the shoot's lower leaves and 
flowering shoots sometimes spring from lateral as well as terminal buds (see Fig. 
41). The tropical almond (Terminalia) has a somewhat peculiar growing and 
fruiting habit, the terminal mixed flower buds being formed on the ends of long 
shoots. When these unfold they give rise to short growths or spurs, in the axils 
of whose upper leaves flowers and fruits are borne. The long growths or shoots 
originate from lateral buds. 

Group IV. — Fruit buds borne laterally, containing flower parts only 
and giving rise to inflorescences without leaves or if leaves are present 
they are much reduced in size. 

In the peach, lateral fruit buds are formed on the long shoots (see 
Fig. 42). Two additional or supernumerary leaves commonly appear 
at many nodes as the season progresses and fruit buds develop in their 
axils. The bud in the axil of the original leaf generally remains a leaf 
bud; rarely it too differentiates flower parts. This whole structure may 
possibly be considered a much reduced secondary growth. Often only a 
single extra leaf develops at the node, in which case only one fruit bud 
forms at that point, that in the axil of the supernumerary leaf. The 
peach also forms fruit buds on secondary or even on tertiary lateral 
branches. As a rule when the fruit buds occur on the upper or outer 
portions of secondary shoots and sometimes on the primary shoots, they 
are single, being differentiated from the bud in the axil of the single leaf. 
They are quite likely to be in pairs at the more basal nodes. As already 
stated, the flower buds of the peach are usually produced on what would 
be called long growths or shoots, though under certain cultural and prun- 
ing treatments many varieties form short laterals that are comparable 
to spurs in every way. The flower bud of the peach produces only one 
flower. Growth is continued by terminal or by lateral leaf buds. 

The sweet cherries and the Domestica and Insititia groups of plums 
form their flower buds for the most part laterally on spurs (see Fig. 
43). These come from lateral buds on the shoots of the preceding season 



402 FUNDAMENTALS OF FRUIT PRODUCTION 

and their new shoots form both terminal and lateral buds on shoots or on 
older wood. 

The almond, apricot, plumcot, the Japanese and American plums, the 
sour cherry, the currant and the gooseberry have a fruiting habit which is 
a combination of that of the peach on the one hand and the sweet cherry 
on the other. They bear in both ways, though certain varieties may 
show a greater tendency in the one direction or the other. As a rule, 
fruit-bud production on shoots gradually gives way to production on 
spurs as the plants become older and less vigorous. Supernumerary fruit 
buds are produced freely at the nodes of the long vigorous shoots of Japanese 
and American plums and in the currant and gooseberry. 






Figs. 43-45. — Diagrams showing (from left to right) bearing habits of sweet cherry, 

raspberry and grape. 

The kumquat (Citrus Japonica) and the northern pawpaw {Asimina triloba) 
differentiate their flower buds in the axils of the leaves on long shoots of the 
current season and the following season these buds give rise to leafless inflores- 
cences. This bearing habit corresponds to that of the sweet cherry, except that 
production of the flower buds is on long rather than on short growths. 

Group V. — Fruit buds borne laterally, unfolding to produce leafy 
shoots that terminate in flower clusters. 

The blackberry, raspberry, dewberry and their hybrids form fruit 
buds either on primary shoots that come up from their crowns or roots 
each year, or on their secondary lateral shoots (see Fig. 44). These 
flower buds develop into leafy shoots with terminal inflorescences and 
individual flowers or flower clusters in the leaf axils. In most varieties 
the entire cane dies after bearing and growth is continued by the forma- 
tion of new canes springing from the crown or roots. 

In the unopened flower bud of the grape (see Fig. 45), the inflores- 
cence is terminal to a leafy shoot also within the bud, like that of the 
raspberry and blackberry. As the bud opens, however, the bud in the 
axil of the topmost leaf of this developing shoot unfolds and continues 
the growth of the shoot. This results in pushing the flower cluster to 
one side so that the inflorescence appears lateral and opposite a leaf. 
Several flower clusters are formed terminally at successive intervals on 



GROWING AND FRUITING HABITS 



403 



the same shoot and in turn are crowded to one side and hence to appar- 
ently lateral positions. As a rule only certain branches or canes of the 
grape bear lateral buds that differentiate flower parts. These branches 
or canes usually arise from buds near the base or in the median portion 
of bearing shoots. What appears to be the bud or "eye" of the grape 
really consists of two or three buds within the one; a well developed 
central shoot and one or two less highly developed lateral growing points. 
In case the central bud develops prematurely and is killed by frost, its 
place may be taken by another of the group. Occasionally the grape 
produces flowering shoots from latent or adventitious buds. 

In the filbert, which has no true terminal buds, some of the more 
apical lateral buds develop into short leafy shoots ending in clusters of 
pistillate flowers (see Fig. 46). Other lateral buds grow out into dwarf 
shoots, which are without normal-sized leaves, are branched and really 
constitute the male inflorescences. These remain dormant until winter 
or early spring when they open to discharge their pollen. At the base 






Figs. 46-48. — Diagrams showing (from left to right) bearing habits of filbert, chestnut 
and walnut. In filbert and walnut B equals pistillate flower buds, C equals staminate 
flower buds; M equals male catkins. 



they may have resting buds which give rise to vegetative or pistillate 
flower-bearing shoots the following year. 

The cashew nut (Anacardium) and the Brazil nut (Bertholletia) also bear 
terminally on shoots from lateral buds. 

In the cherimoya, pond-apple, sour-sop, sugar-apple and various other 
Anonaceous fruits the fruit buds are borne laterally and the inflorescences 
terminally, with the growth of the flowering shoots proceeding much as in the 
grape. Here the' flowers and fruits appear to be between nodes, or extra-axillary. 
Not infrequently they develop on short spur-like branches. 

In the blueberries the inflorescences develop both terminally and in 
the axils of leaves on new shoots springing from lateral buds. This bear- 
ing habit is a combination of the typical conditions found in Groups V 
and VI as here classified. Ordinarily there are no true terminal buds in 
this group but if terminal buds are formed they are usually fruit buds. 
In Vaccinium atrococcum the flowering shoot has no foliage. Fruit bud 
differentiation apparently takes place in late fall in the axils of leaves 
near the end of the shoot. 



404 FUNDAMENTALS OF FRUIT PRODUCTION 

The European cranberry (Vaccinium oxycoccus), litchi (Nephelium litchi) 
and sea-grape (Coccoloba uvifera) have similar bearing habits. 

Group VI. — Fruit buds borne laterally (or pseudoterminally), unfold- 
ing to produce leafy shoots with flower clusters in the leaf axils. 

In the persimmon any lateral bud and not infrequently adventitious 
or dormant buds on 2-year-old or older wood, may become a fruit bud. 
The following year these unfold and form leafy shoots with solitary 
pistillate or with clusters of staminate flowers in the axils of the more 
basal leaves. The male and female flowers may be borne on the same 
tr.ee or on different trees. 

The mulberry has a similar bearing habit, except that both pistillate 
and staminate flowers are usually borne on the same flowering shoot. 
The male flowers are formed in the axils of the more basal leaves and the 
pistillate flowers in the axils of higher leaves. 

In the American cranberry (Vaccinium macrocarpon) the flowering 
shoots arise from lateral buds on the creeping vegetative branches. The 
flowers are borne singly in the leaf axils. 

The chestnut, chinquapin, oak and beech have very similar bearing 
habits (see Fig. 47). The pseudoterminal or more apical lateral 
buds, when they differentiate flower parts, give rise to shoots in the axils 
of the leaves. Male catkins appear in the lower axils and female, or 
mixed male and female, clusters above them. Sometimes dwarf shoots 
arise from the basal buds in the chestnut and produce male catkins only 
in the leaf axils. True terminal buds are sometimes formed in the oak 
and beech and these may be fruit buds. In the beech there are short 
spur-like growths Which have no lateral buds except a single pseudo- 
terminal bud. This is never a flower bud. 

The fig bears lateral fruit buds. Its pseudoterminal bud, which is usually 
larger than the others, is generally vegetative. Frequently more than one 
bud is formed in a leaf axil and they appear in pairs, side by side. The fruits are 
formed singly in the leaf axils. The fig can bear three (or more, according to 
some authorities) distinct crops in a year. 

In the avocado the lateral flower buds give rise to flowering shoots in which 
the inflorescences are in the axils of the more basal leaves. 

The pistachio (Pistacia vera) and star apple (Chrysophyllum) have a similar 
bearing habit and the olive, which has been mentioned as belonging in Group 
III, might as readily be included here, since it produces lateral as well as terminal 
flower buds. 

In the jujube (Zizijphus jujube) several flowering branches may arise at a 
single node. Solitary flowers are borne in the leaf axils of these branches. After 
the ripening of the fruit the leaves and fruit fall off and finally the entire branch 
falls. Buds for the following crop are differentiated on strictly vegetative 
branches. There is thus a definite dimorphism of branches in this species, the 
fruiting branches being deciduous and not forming a part of the permanent 
framework of the tree. 



GROWING AND FRUITING HABITS 405 

Group VII. — Fruit buds borne both terminally and laterally, inflo- 
rescences generally terminal. The fruits that are discussed here might 
be included with those of Groups II and IV for they represent a combi- 
nation of those two fruiting habits, but for convenience they are con- 
sidered separately. 

In the walnut, hickory and pecan the terminal bud may give rise to 
a short leafy shoot ending in a female inflorescence (see Figure 48). The 
male flowers are borne on leafless inflorescences arising from lateral 
buds not far below the terminal. In the walnut there are two superposed 
buds in each leaf axil, the upper being usually the first to open. At a 
single node two male inflorescences may appear simultaneously from the 
two buds, or a leafy shoot may come from the upper and an inflorescence 
from the lower. In the hickory the male catkins are sometimes borne 
in the axils of the basal leaves on the terminal shoot, resulting in the pro- 
duction of male and female flowers on the same shoot. 

Group VIII. — Fruit buds adventitious. Since adventitious fruit 
buds are necessarily lateral, the plants included here might readily be 
classed with those of Groups IV, V or VI. However, this bearing habit 
is more or less distinct and these fruits may well be placed in a separate 
class. 

The jaboticaba and cambuca form adventitious flower buds on their trunks, 
main and smaller limbs and even on their exposed roots. These produce no 
leaves when they open. 

The cacao bears in the same way, though the flower buds appear first on the 
trunk and as the trees grow older, on the whorled branches. 

The coffee produces fruiting branches from adventitious buds at the nodes. 
The upper bud becomes a horizontal fruit-bearing branch, the lower an upright 
vegetative shoot. 

Group IX. — There is another group of plants which have fruit buds 
in the axils of the leaves and in which these buds unfold and develop 
their flowers and fruits very soon after the flower parts are differentiated. 
However, it is not possible to draw a clear line between this fruiting 
habit and that described for Group IV. 

This group includes the passion fruit (Passiflora), the papaya (Carica papaya) 
and many others with a more or less herbaceous type of growth. In culture, 
as well as in growing and fruiting habits, these plants resemble certain vegetables 
more closely than deciduous fruits. 

The Relation of Fruiting Habit to Alternate Bearing. — Terminal 
fruit bud formation often has been regarded as an explanation of the 
alternate bearing frequently occurring in species or varieties with 
this fruiting habit. However, not all the terminal buds on shoots and 
spurs of plants with a terminal-fruit-bud-bearing habit develop into 
fruit buds at one time. Many are leaf buds and unfold leafy non- 



406 FUNDAMENTALS OF FRUIT PRODUCTION 

flowering shoots or spurs. Fruit bud differentiation depends . on 
nutritive conditions in and about the terminal bud at such time or times 
when differentiation can take place. Terminal bearing involves a definite 
limitation to shoot or spur extension in a straight line. New vegetative 
extension must be from lateral buds if all terminals form fruit buds in 
one season, but this seldom occurs and those buds that do not become 
fruit buds one year may therefore become differentiated into fruit buds 
the next season. In this way regular annual bearing is possible if nutri- 
tive conditions within the plant remain such that fruit bud differentia- 
tion can occur each year. Even if all terminals were to differentiate 
fruit buds one season and to flower and fruit the next, there would still 
be opportunity for the formation of another set of fruit buds terminally 
on the new shoots or new spurs. Therefore regular annual bearing would 
still be possible provided nutritive conditions were favorable. The 
terminal fruiting habit does not in itself lead to alternate bearing except 
in the event that practically every terminal forms a fruit bud one season 
and sets fruit the next while at the same time growing conditions this 
second season prevent fruit bud differentiation on the new shoots or 
spurs developed from lateral buds. When this extreme is encountered 
it should be handled as a problem in nutritive conditions to be corrected 
by the control of environmental factors. In other words, though many 
varieties of plants which bear fruit buds terminally are much inclined 
to alternate bearing, that tendency is not a necessary product or accom- 
paniment of terminal fruit bud formation. 

Obviously the production of fruit buds laterally on either spurs or 
shoots makes every provision for regular annual bearing, not only of 
the plant as a whole, but of the individual part, if conditions within the 
plant are favorable for fruit bud differentiation. 

Regularity of bearing, therefore, is a cultural problem, to be dealt 
with by influencing nutritive conditions. Attention is given to this 
phase of the question in the section on Nutrition. 

Possible Causes of Different Bearing Habits. — Knowledge of bearing 
habits is decidedly fragmentary and little is known concerning the factors 
which may control it or influence it in any way. However, it is known 
that the apple with its characteristic terminal fruit bearing habit stores 
the bulk of its starch in the pith while the peach with its characteristic 
lateral fruit bearing habit stores the bulk of its starch in the leaf gaps. 
Since carbohydrate, and particularly starch, accumulation is so closely 
associated with fruit bud differentiation, at least in the apple, it is 
possible that anatomical structure may have much to do with the region 
of starch storage and that this in its turn may be an important factor 
determining the bearing habit. 

Summary. — The general purpose of all pruning is to increase yields, 
improve grades and reduce production costs. These objects may be 



GROWING AND FRUITING HABITS 407 

attained either through modifying the form or through influencing the 
functioning of the tree as a whole or of its individual parts. Pruning 
for form is essentially training. Training seeks directly to secure the 
distribution of the fruit bearing parts that is most advantageous for 
economy of production, disease and insect control, for minimum loss 
from breaking of limbs and for proper coloration. These ends are fur- 
thered by (1) heading the tree properly, (2) providing a reasonable 
number of well-spaced scaffold limbs, (3) preventing the formation of 
weak crotches, and (4) keeping the tops of the trees from growing too 
high or spreading too far. Pursuant to these aims the plants are generally 
trained in one or another of several standard shapes. Thus training 
results in a certain degree of uniformity of appearance in the orchard. 
The bearing habits of most species and varieties are fairly well fixed, 
though they are subject to some modification by pruning and other 
cultural treatment. Fruit buds are differentiated either terminally or 
laterally and when they open they may give rise to (1) leafless flower 
clusters, (2) leafy growths with terminal flower clusters, or (3) leafy 
growths with lateral flower clusters. There are thus six distinct bearing 
habits and in addition a number of combinations between these types. 
The more common fruits are classified in respect to their bearing habits. 
Alternate bearing is not a necessary product of any type of bearing. If 
nutritive conditions within the tree are favorable fruit buds may be 
formed every year. Consequently alternate bearing is a problem in 
nutrition. Different bearing habits are probably associated with differ- 
ent methods or places of food storage. 



CHAPTER XXII 
PRUNING— THE AMOUNT OR SEVERITY 

Pruning can vary in three major respects and in three only. It can 
vary: (1) in amount or severity, (2) in kind or distribution and (3) in the 
season at which it is done. Characteristic responses by the plant are 
to be expected not only as the pruning varies in any of these three respects 
but according to fruiting habit and as the plant itself varies in age, vigor 
and nutritive condition. These three major aspects of pruning are dis- 
cussed in the order in which they have been mentioned. 

A search through horticultural literature reveals a great diversity of 
opinion as to the influence of varying amounts of pruning on growth and 
productiveness. Some have considered heavy pruning a great stimulant 
to vegetate growth especially, though perhaps having the opposite effect 
on fruit production. This idea is reflected in the phrase "prune in the 
winter for wood." Others have regarded pruning of any kind and more 
particularly, pruning in any amount, as a harmful practice because it has 
been thought to check growth. Most of these partly accepted ideas have 
been based upon theoretical considerations or field observations, of which 
some have been sound and accurate but many have been either fallacious 
or inaccurate or have failed to consider other important facts. Not until 
comparatively recent years have exact and pertinent experimental data 
been available. 

Influence on Size of Tree. — Bedford and Pickering 4 were among the 
first to make a careful study of the different effects of various amounts of 
dormant season pruning on the apple. Table 1 shows the mean tree 
size and weight for all varieties studied and given different pruning treat- 
ments covering a period of ten years. The figures for tree size take into 
consideration spread and height and trunk circumference. Clearly these 
show that the unpruned tree increases in size and weight more rapidly 

Table 1. — Influence of Amount of Pruning on Tree Size in the Apple 

(After Bedford and Pickering 4 ) 

Very Little or no Pruning Moderate Pruning Hard Pruning 

Tree size relative. .106 100 82 

Tree weight relative 120 100 84 

than the pruned tree and that the heavier the pruning the more pro- 
nounced is the check upon growth. In commenting on the somewhat 
greater influence of pruning on weight than on size revealed by the figures 
in the table Bedford and Pickering remark, "This increase in weight 
must be due to an increase in weight of the stem and main branches, for it 

408 



PRUNING— THE AMOUNT OR SEVERITY 



409 



cannot be accounted for merely by the weight of wood removed during 
pruning: the prunings would, on an average, have amounted to 27 
pounds per tree during the ten years in the case of the moderately pruned 
trees, whereas these trees at the end of this time showed a deficit of 49 
pounds as compared with the unpruned ones." Gardner 21 in Oregon and 
Alderman and Auchter 1 in West Virginia (see Table 2), both working 
with young apple trees, obtained results leading to the same conclusions. 
The unpruned tree increases in size more rapidly than the moderately 
or heavily pruned tree, not because it produces more new shoot growth 
each year, but because it losses none by pruning. Tufts, 47 in California, 
studying the influence of varying amounts of pruning on newly set 
apricots, sweet cherries, peaches, pears and European and Japanese 
plums found, in every instance, less rapid increases in trunk circumference 
with each increase in the severity of the pruning (see Table 3). Since 
he found correlation coefficients ranging from 0.83 to 0.92 for trunk cir- 
cumferences and weights of top and coefficients ranging from 0.76 to 
0.84 for trunk circumferences and weights of root, depending on the 
species, it is evident that trunk circumferences may be taken, other 
things equal, as fairly accurate indices to tree size. Consequently his 
data, together with those of the investigators already cited, are evidence 
that, in general, pruning results in a check to increase in size. At least 
it may be considered established that this holds for deciduous tree fruits. 

Table 2. — Influence of Amount of Pruning on Size of Young Apple Trees 
{After Alderman and Auchter 1 ) 



Variety 



Type of 
pruning 



Number 
of trees 



Height 

(in feet) 



Spread 
(in feet) 



Stayman 

Stayman 

Stayman 

Rome 

Rome 

Rome 

Gravenstein 

Gravenstein 

Gravenstein 

Stark 

Stark 

York, Grimes and Rome 
York, Grimes and Rome 
York, Grimes and Rome 



Heavy 

Moderate 
Light 

Heavy 

Moderate 
Light 

Heavy 

Moderate 
Light 

Heavy 

Light 

Heavy 

Moderate 

Light 



24 
19 
19 

13 

8 

11 

17 

7 

10 

19 

4 

7 
5 
6 



7.32 
7.89 
9.50 

7.45 
8.18 
9.16 

7.43 
6.83 
8.94 

7.57 
10.79 

9.55 

9.73 

10.50 



5.29 
5.52 
5.75 

3.68 
4.17 
4.23 

4.05 
4.19 
4.34 

5.17 

6.85 

4.83 
6.17 
7.10 



410 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 3. — Increase in Trunk Circumference under Varying Pruning 

Treatments 
(After Tufts") 



Kind of fruit 



Pruned 


Pruned 


Pruned 


severely 


moderately 


lightly 


(centimeters) 


(centimeters) 


(centimeters) 


11.7 


12.6 


15.3 


10.0 


11.2 


12.3 


12.0 


16.9 


19.4 


8.7 


9.1 


9.7 


6.3 


10.4 


11.3 


7.2 


8.8 


9.4 


6.2 


7.1 


8.4 


8.9 


10.9 


12.3 



Apricot (Royal) . . . 
Cherry (Napoleon) 
Peach (Elberta) . . . 
Pear (Bartlett) .... 
Plum (Climax) .... 

Plum (Pond) 

Prune (French) 

Average 



Amount and Character of New Shoot Growth. — The framework of the 
tree is developed from its shoots of the preceding or earlier years. Since 
the general influence of pruning is to check increase in size, it might be 
reasoned that it results in a corresponding decrease in the amount of new 
shoot growth produced each year. On the other hand it is possible that 
the check to increase in size might be due largely, or even entirely, to the 
annual removal of wood. Experimental data on this question were 
obtained by Bedford and Pickering. 4 They selected a number of shoots 
in a tree, all as nearly as possible of uniform length (about 36 inches) and 
thickness. Some were pruned back to a length of 6 inches, some to 
12 inches, some to 24 and some had only their terminal buds removed. 
Table 4 shows the relative numbers, lengths and weights of the new side 
shoots that were formed and also the influence of these treatments on the 
parent branch. Heavy pruning back resulted in fewer side shoots with 
less total length and less weight than lighter pruning or than none at 
all. The greatest decrease was in the number of new shoots, from 
which it may be inferred that individually these shoots were somewhat 
longer and stronger than those on the lighter pruned limbs. The differ- 

Table 4. — Effects of Pruning Back Individual Shoots Varying Amounts 
(After Bedford and Pickering 4 ) 

Length of shoot after pruning, in inches 6 12 24 36 

Weight of original shoot and laterals (relative) 100 179 310 562 

Thickening of the original shoot (relative) 100 114 117 129 

New shoots formed: 

Number (relative) 100 116 198 292 

Length (relative) 100 113 145 183 

Weight (relative) 100 108 123 142 

ence in weight of old wood after a year's growth is particularly striking, 
the unpruned trees having over five times the amount of those pruned 



PRUNING— THE AMOUNT OR SEVERITY 



411 



heavily. These same investigators found, however, that in mature 
trees that had been bearing for a number of years heavy priming resulted 
in almost twice as much new shoot growth as was produced by unpruned 
trees. 

On the other hand Blake and Connors, 7 in New Jersey, found that 
pruned peach trees produced in the first year somewhat more new shoot 
growth than unpruned trees. The average for the latter in their Vineland 
experiment was 695 inches and for the pruned trees (all treatments) 
753 inches. In West Virginia, Alderman and Auchter 1 report that heavy 
pruning of the apple resulted in somewhat greater new shoot growth for 
the first 2 or 3 years, but that greater shoot development accompanied 
lighter pruning as the tree became older (see Table 5). Gardner 22 
in Oregon, likewise working with young apple trees, found that different 



Table 5.- 



-Effect of Light and Heavy Pruning on New Shoot Growth in 
Apples of Different Ages 
(After Alderman and Auchter 1 ) 





Pruned heavily- 


Pruned lightly 


Gain over heavy 
pruning (feet) 


Season 


Average total 
length, feet 


Average total 
removed, feet 


Average total 
length, feet 


Average total 
removed, feet 


1911 


4.41 


3.30 


5.58 


3.44 




1912 


16.25 


12.91 


15.51 


4.78 


-0.74 


1913 


41.53 


33.16 


34.33 


13.89 


-7.20 


1914 


84.08 


49.17 


99.39 


22.12 


15.31 


1915 


161.74 




224 . 89 




63.15 



varieties respond in a quite dissimilar manner to pruning of the same 
severity. His data, some of which are summarized in Table 6, show that 
lightly or moderately pruned Grimes produced more shoot growth 
annually than unpruned trees, but those heavily pruned produced dis- 
tinctly less than the check trees. On the other hand the heavily pruned 
Romes produced more shoot growth annually than those pruned moder- 
ately or not at all, while on the whole the severity of annual pruning 
seemed to make but little difference in the amount of new shoot growth 
in Gano and Esopus. At first these data may seem so contradictory 
that no conclusion or interpretation is possible. However, attention 
may be called to the great variations shown by young apple trees of 
different varieties in their growing habits and to the change in these 
differences with age. Thus there is a great dissimilarity between young 
trees of Rome and Grimes in the number of spurs and the peach usually 
produces no true spurs. When these peculiarities of age and variety are 
considered along with the data that follow on the influence of various 
pruning treatments on fruit spur and fruit bud production the contradic- 
tions that have been noted do not appear so puzzling. 



412 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 6. — Effect of Light and Heavy Pruning on New Shoot Growth in 

Young Apples of Different Varieties 

(After Gardner—) 



Variety 


Number of 
trees aver- 


Severity of 
annual prun- 


Average 1914 
shoot growth, 


Average 1915 Average 1916 
shoot growth, shoot growth, 


Average 

number fruit 

spurs in fall 

of 1916 




aged 


cent. 


centimeters 


centimeters 


centimeters 




71 
38 


none 
0-25 


492 
675 


1762 
2251 


3852 
4713 


402 




457 




55 


26-50 


714 


2401 


4913 


341 


Grimes 


75 


51-75 


378 


1339 


2818 


116 


Gano 


32 


26-50 


456 


2493 


5435 


158 


Gano 


14 


51-75 


561 


2464 


5459 


111 




28 


none 


629 


2051 


3520 


142 


Rome 


36 


26-50 


508 


1973 


3634 


34 


Rome 


29 


51-75 


845 


2541 


4630 


31 




27 


none 


583 


2121 


2287 


505 


Esopus 


56 


46-76 


453 


1736 


3077 


134 



In recapitulation it may be said that different species and varieties 
show great variations in their response by new shoot production to prun- 
ings of like severity. These differences are due primarily to growing 
and fruiting habits and secondarily to age, vigor and nutritive conditions, 
as well as to environmental conditions with which they may happen to be 
associated at the time. 

Leaf Surface and Root System. — Any practice that would effect a 
reduction in the amount of new shoot growth and perhaps of spurs as 
well, would be expected to result in a corresponding decrease in leaf 
area and in root development. Chandler's 11 investigations of the rela- 
tion of certain pruning practices to subsequent root development show 
this reduction. Some of his data are summarized in Tables 7 and 8. 



Table 7. — Influence of Varying Amounts of Pruning on Subsequent Leaf 

and Root Development 







(After 


Chandler 11 








Treatment 


Number of 
trees 


Average leaf 
surface be- 
fore pruning, 

May 23, 

1918 (square 

inches) 


Average leaf 

surface after 

pruning, 

May 23, 

1918 (square 

inches) 


Average leaf 

surface, 

Sept. 17, 

1918 (square 
inches) 


Average root 

weight 

May 19, 

1919 (grams) 


Average top 
weight, 
May 19, 
1919 in- 
cluding prun- 
ings (grams) 


Unpruned 

Little pruning. . 
Much pruning. . 


41 

33 

• 39 


756.48 
819.14 

775.70 


756.48 
470 . 27 
291.61 


1737.94 

1219.80 

895.96 


208.5 
166.9 
126.3 


684.0 
558.3 
494.3 



In commenting on the data presented in Table 8, Chandler 11 says: 

"It will be seen that in all cases the leaf surface has been rather markedly 
reduced. On the other hand except in case of the summer-pruned trees, when 



PRUNING— THE AMOUNT OR SEVERITY 



413 



Table 8. — Effect of Pruning on Leaf Surface and Top and Root Growth of 
Peach Trees 4 Years Old at Beginning of Experiment 

(After Chandler 11 ) 



Treatment 



Average leaf sur- 
face in 191G 



June, 
square 
inches 



Sep- 
tember, 
square 
inches 



Average leaf sur- 
face in 1917 



June, 

square 

inches 



Sep- 
tember, 
square 
inches 



Tree, 
weight, 
pounds 



Weight 
prun- 
ings, 

pounds 



Root 
weight, 
pounds 



Elberta: 

Pruned 1916 and 1917 

Unpruned 

Crawford Early: 

Pruned summer 1910, spring 
1917 

Unpruned 

Pruned spring 1917 

Unpruned 



14,239 
24,771 



2,202 
17,886 



80,659 
97,850 



50,034 
85,721 



31,209 59,579 
98,169 116,344 



18,904 
74 , 389 
40,681 
114,516 



68,070 
142,920 

79 , 563 
144,911 



96.3 
116.3 



75.8 
111.9 
126.3 
131.7 



116.4 
116.3 



97.4 
111.9 
134.7 
131.7 



27.4 
37.3 



20.9 
34.6 
34.9 
44.9 



the weight of the prunings has been added to that of the tree, the total weight 
of pruned and unpruned trees is practically the same. The root growth, how- 
ever, has been greatly reduced. When it is considered that this reduction in 
growth has occurred during the last 2 years of the 6 years during which the trees 
have been in the orchard, it will be realized how striking the reduction is. Thus 
if at the beginning of 1916 the roots weighed 15 pounds, then the root growth 
on the unpruned trees since that time has been nearly twice that on the pruned 
tree. Unfortunately we have no records as to the root weight of trees 4 years 
old, but it must have been 10 pounds or more, since by records that we have the 
tops would then have weighed from 30 to 35 pounds. If the root weight at the 
beginning was 10 pounds, then the root growth in the pruned trees since that 
time has been but 65 per cent, of that made by the unpruned trees." 

In effect the influence of a heavy top pruning on the subsequent 
development of the tree is more or less comparable to that of a root 
pruning. 

Presumably, pruning practices which do not reduce top growth in 
trees of other kinds or of greater age than those studied would not have 
such an influence on root growth; exact data, however, are lacking. It 
is significant, nevertheless, that in young trees pruning of the top has 
been found greatly to influence the extent of root development the 
following season. This suggests one of the indirect ways through which 
pruning one season may influence growth and development 2 or 3 years 
later. 

Influence on Fruit Spur and Fruit-bud Formation. — In Table 6 
are presented data on the influence of varying amounts of pruning on 
fruit spur formation in young apple trees. The less the pruning the larger 
is the number of fruit spurs formed. With very severe pruning there is a 



414 FUNDAMENTALS OF FRUIT PRODUCTION 

great reduction, the checking influence differing greatly with the variety, 
however. Varieties like Esopus and Grimes, that are much inclined to 
develop spurs at an early age, show a relatively greater check in this 
respect than those like Rome and Gano that as young trees produce 
comparatively few spurs. In any case, however, pruning tends to reduce 
their number. Data are presented showing also that severe pruning acts 
in a similar manner in decreasing the numbers of fruit buds that form 
on the spurs. 22 Similar data on fruit bud formation in young apple 
trees have been obtained in West Virginia 1 and in England. 4 The ratio 
of flower clusters for the years 1909-1914 obtained by the English 
investigators in one of their experiments was 52 for hard pruning, 100 
for moderate pruning and 180 for no pruning. There were corresponding 
differences in total yield. All these investigators show that heavily 
pruned trees may be expected to come into bearing more slowly than 
those pruned moderately, lightly or not at all. 

On the other hand, heavy pruning does not always result in decreased 
yields. Data obtained in an experiment with Arkansas and York 
Imperial apple trees that had been bearing for a number of years and 
were somewhat lacking in vigor, summarized in Table 9, show steady 
increments in yield with each increase in the severity of the pruning. 1 

Table 9. — Influence of Pruning on Yields in a Declining Apple Orchard 

{After Alderman and Auchter 1 ) 



Arkansas, 1914-1915 
crops (bushels per tree) 



York, 1914 crop 
(bushels per tree) 



Heavy pruning. . . . 
Moderate pruning. 
Light pruning 



9.65 
8.20 

7.89 



14.02 

11.94 

9.15 



The heavy pruning must have had the effect of reducing somewhat the 
total number of fruit spurs, at least in comparison with the trees pruned 
more lightly. Consequently the increased yields must have been due 
either to the formation of a larger number of fruit buds or to the better 
setting of the blossoms. This is an influence not unlike that already 
pointed out as very frequently attending the judicious use of nitrogenous 
fertilizers. 

Influence on Leaf Area and Fruit Size. — In Table 10 are presented data 
on the influence of varying amounts of pruning on average size of leaf 
and total leaf area in apple trees. Not only are the individual leaves of 
the heavily pruned trees larger than those of the unpruned or lightly 
pruned trees, but there are more of them. Consequently such trees 
have a materially increased leaf surface. This in turn creates a greater 
requirement for nutrients and for moisture; if this requirement is met, an 
increased production of elaborated foods may be expected. 



PRUNING— THE AMOUNT OR SEVERITY 



415 



Table 10. — Influence of Pruning on Leaf Size Area 
(After Alderman and Auchter 1 ) 



Average leaf area (square 
inches) 



Lupton 
orchard 



Grimes 
orchard 



Total leaf area per tree 
(.square feet) 



Lupton 
orchard 



Grimes 
orchard 



Heavy pruning . . . 
Moderate pruning 
Light pruning 



2.77 
2.37 
2.10 



4.99 

4.18 
3.52 



610.8 
432.2 

418.7 



1143.8 
911.5 
659.6 



The decrease in size of fruit recorded by Bedford and Pickering 4 
as accompanying severe pruning probably is explained by the increased 
leaf area of the trees and the consequently greater requirement of this 
foliage for water — a requirement that under the conditions of the experi- 
ment the roots were unable to supply. Experience and observation 
generally indicate that pruning does not decrease size of fruit. As 
a matter of fact it often has the opposite effect. Perhaps this tendency 
is most clearly shown in such fruits as the raspberry, blackberry and grape 
which in the absence of pruning are inclined to set more fruit than they 
can mature properly, especially when supporting the large amount of 
barren wood which unpruned plants of these species characteristically 
bear. Within certain rather wide limits the general influence of pruning 
is to reduce, through the removal of actual or potential bearing wood, 
the amount of fruit that can set. It tends also to enlarge leaf area 
and thus, though its effects are concentrating, it at the same time increases 
the requirement for nutrients and moisture. If these are available in ample 
quantities pruning may result in an increase in size of fruit; if they are 
lacking it may result in a reduction. Though the general tendency of 
pruning, as of fertilization, is to increase the size of the fruit, its influence 
in this regard is not direct. Nevertheless it is one of the most important 
means at the grower's disposal for this purpose. This is particularly 
true for those species or varieties with which thinning of the fruit is 
impracticable. 

Pruning as a Cause of Abnormal Structures. — In the sections on 
Water Relations and Nutrition attention is directed to certain patho- 
logical conditions that may result from extremes of moisture or from an 
unbalanced nutrient supply. Pruning may disturb both the water and 
food relations of the plant; hence certain pathological conditions may 
follow, particularly from heavy pruning. Daniel, 16 who has given this 
question considerable attention, enumerates a rather large number of 
monstrosities more or less directly attributable to pruning. Among the 
more important of these maybe mentioned the forcing out of the so-called 
."second-bloom" from the limbs and trunks of pear trees, marked 



416 FUNDAMENTALS OF FRUIT PRODUCTION 

increases in size and changes in the form of leaves, fasciation and the 
metamorphosis of the glands of apricot leaves into small leaflets. He 
considers these abnormalities to be due to an upsetting of the balance 
normally existing between transpiration and assimilation. It should be 
remembered, however, that in many instances these abnormal structures 
arise independent of any pruning. 

Amount of Pruning Varying with Fruiting Habit. — The facts just 
presented on the results to be expected from light, moderate, heavy 
or no pruning, show clearly that no rigid rules can be stated as to the 
amount of pruning best suited to orchard trees even of a single age or of a 
single kind. However, if certain other pertinent facts and principles 
be considered, the amount to be given orchard trees becomes somewhat 
more easily determined. 

The fruit grower wishes to produce as soon as possible a tree, shrub, 
or vine sufficiently large to bear crops of at least moderate size. It is 
necessary, furthermore, that the plant have a strong framework for the 
support of the smaller branches and their fruiting wood and that it be 
adequately equipped with the spurs or shoots that bear fruit buds. For 
the first year or several years, in many species, fruit production is neither 
expected nor desired. The maturing of fruit and to a certain extent even 
the formation of fruit buds and potential fruiting wood might tax the 
energies of the plant so that increase in size would be checked seriously. 
A little later, however, when the tree approaches such age and size that it 
can begin production without injury to its general welfare the grower 
desires it to develop gradually (or sometimes quickly) fruit-producing 
growth and he wishes to keep this growth actively at work. As the 
tree becomes still older its natural growing habits are very likely to 
encumber it with too much fruiting wood, more than its roots and leaves 
can supply with food materials for heavy and regular production. The 
grower's aim then should be to get rid of the old unproductive wood 
or to invigorate it or to limit the formation of new wood. His problem 
is first that of building the plant; then it is equipping it and providing 
for such extensions and new equipment as space and conditions permit 
and finally it becomes a problem of maintenance at maximum efficiency. 

When these general principles are considered in their relation to the 
varying results attending pruning in different amounts, it is evident that, 
in general, tree, bush and vine fruits should be pruned heavily when young 
to secure a strong, stocky framework with well spaced limbs and — of 
equal importance — to prevent the production of fruit and even of fruiting 
wood As the plant approaches bearing age and size, pruning should be 
less severe, to permit or encourage the production of fruiting wood. 
Perhaps in extreme cases it may be desirable at this stage to do no pruning 
at all. As the plant becomes still older, pruning is again increased in 
severity, thus limiting or sometimes reducing the amount of fruiting. 



PRUNING— THE AMOUNT OR SEVERITY 



417 



wood and in this way concentrating the energies of the tree upon a better 
support of what is left. The lower line shown in Fig. 49 gives graphically 
some idea of the manner in which the amount of pruning should vary with 
age in the average apple, pear, plum or cherry tree which is rather slow 
growing at first and bears principally on spurs. Of course as the trees 
vary in vigor, rapidity of growth, fruiting habits and in other respects 
there should be accompanying changes in the severity of the annual 
pruning. Thus the peach ordinarily begins bearing at an earlier age 
than the apple or cherry. Consequently it should be pruned to leave 
fruiting wood and permit bearing earlier. Furthermore, since it bears 
fruit only on shoots of the preceding year, regular production depends 
on annual provision for a good supply of new shoots. If these are to be 
produced on the lower part of the tree where the weight of the fruit will 
not place an excessively severe strain upon the crotches comparatively 
heavy annual pruning is necessary. At no stage in the life of the peach 



85 

75 

65 

?55 

■§45 

a. 35. 

25 

15 

5 









































^£Oy 
























■ 














go 
















V 











































Age 

Fig. 49. — Graphs showing relative amounts of pruning required for the peach and apple at 

different ages. 



tree is it necessary practically to discontinue pruning in order to develop 
fruiting wood and bring it into bearing. The upper line in Fig. 49 
shows roughly how the amount of pruning desirable for trees of this kind 
varies with age. Similarly it is possible to draw graphs for the amounts 
of pruning required by trees of other kinds. It should be emphasized, 
however, that these will vary in details not only with different kinds of 
fruits, but with varieties of the same kind and for the same variety 
from place to place and under varying soil and environmental conditions. 
Summary. — By and large, unpruned trees increase in size more rapidly 
than pruned trees of the same kinds and the dwarfing effect of pruning 
is more or less directly proportional to its severity. This dwarfing 
effect is a result not so much of the production of less new shoot growth 
each year as of the amounts of wood removed. The dwarfing effect 
of top pruning extends to the root system because of the reduction in 
total leaf area. Pruning generally results also in a diminution in 

27 



418 FUNDAMENTALS OF FRUIT PRODUCTION 

the number of fruit spurs in spur producing species, though there may 
or may not be a corresponding reduction in number of fruit buds and 
in the resulting yield. Within certain limits it tends to increase the 
size of the fruit. Extremely heavy pruning may occasionally result 
in different types of abnormal growth, such as fasciation. The severity 
of pruning that is desirable depends on many conditions, the age of 
the tree and its bearing habit being among the more important. 






CHAPTER XXIII 
PRUNING— THE METHOD 

It seems strange that a horticultural practice as old as pruning should 
have come down to the present with so little realization that it includes 
questions of kind as well as of amount and of season. Nevertheless, most 
of the literature is silent on this matter, as though all pruning were 
necessarily the same in kind, except perhaps for the innumerable detailed 
ways of cutting to certain buds or of leaving certain spurs or shoots for 
replacement purposes. The fundamental differences between essen- 
tially distinct practices have not been generally recognized. Instead, 
attention has been focused upon the minute and less important details 
of procedure. Without doubt this lack of realization that pruning may 
vary greatly in kind and that entirely different results attend distinct 
kinds or types of pruning has been responsible for much of the confusion 
and apparent contradiction that is evident on comparison of the reports 
of various writers and investigators. 

Heading Back and Thinning Out. — A number of classifications of 
pruning as to kind are possible. However, none is more serviceable than 
one which recognizes the difference between heading back and thin- 
ning out. It is difficult, if not impossible, to differentiate absolutely 
between the two for sometimes the removal of a branch or part of a 
branch is at the same time a thinning out and a heading back. In 
general, however, the differences between the two are clear and evident 
even to a casual observer. Thinning out removes entirely a shoot, spur, 
cane, branch, limb, or whatever the part may be; heading back removes 
only a portion, leaving another portion from which new growths can 
develop. 

Influence on New Shoot and New Spur Formation. — Theoretically a 
heading back that is equal in severity to a certain thinning out removes 
approximately the same amount of wood and the same number of buds. 
In practice however, there is a considerable difference. A thinning out 
that removes 50 per cent of the shoots, gets rid of just half the amount 
of wood of the past season and just half of the total number of buds, 
both lateral and terminal. On the other hand a 50 per cent heading 
back removes somewhat less than half the weight of woody tissue formed 
the past season and somewhat more than half the total number of new 
buds, for it removes an equal number of the lateral buds and all the 
terminals. A heading back that is equal in severity to a certain thinning 

419 



420 



FUNDAMENTALS OF FRUIT PRODUCTION 



out is therefore more severe in one respect and less severe in another. 
If the pruning is comparatively heavy the difference is slight, but if the 
pruning is light the difference is correspondingly greater. 

Observation shows that when growth begins the terminal and sub- 
terminal buds are usually the first to start and in the majority of decidu- 
ous trees and vines (less frequently in shrubs) they produce the longest 
and strongest shoots, though shoots may grow from many of the lower 
buds. However, seldom do all the lateral buds start and as a rule the 




Fig. 50. — Grimes apple tree, showing a typical response to heading back. Compare with 

Fig. 51. 



largest percentage of those that remain dormant are on the basal portion 
of the shoot. Those species that bear principally on spurs form these 
spurs mainly from buds on the median and terminal portions of the 
shoot. Heading back, therefore, limits fruit spur formation to a greater 
extent than a correspondingly heavy thinning out. This is obvious 
from the data presented in Table 11, showing the amounts of shoot 
growth and the numbers of spurs formed by vigorous 5-year-old apple 
trees of different varieties that had been headed back or thinned out 



PRUNING—THE METHOD 



421 



with equal severity. However, the influence on fruit-spur formation 
of heading as compared with thinning out is much more pronounced in 
some varieties than in others. Gano, for instance, showed practically 
no difference in this respect. 

Even more striking than the inequality in numbers of spurs from the 
two kinds of pruning was that in the amount of new shoot growth. 
Heading back invariably led to greater shoot production than a corre- 
sponding amount of thinning out (see Table 11). In Esopus the amount 




Fig. 51.- 



-Grimes apple tree, showing a typical response to thinning out. 

Fig. 50. 



Compare with 



of new shoot growth was almost double that in the thinned trees. Appar- 
ently thinning out some of the shoots in a tree does not result in diverting 
the same amount of food and moisture they would have used into the 
remaining unpruned shoots. Certainly it does not result in a suffi- 
ciently increased new shoot growth from them to compensate for that 
which would ordinarily have grown from the portion of the top that 
has been pruned away. It has some stimulating influence of 
this kind but it also results in a reduction in the total new growth formed. 



422 



FUNDAMENTALS OF FRUIT PRODUCTION 



On the other hand heading back has a more stimulating influence and 
the pruned shoots tend to give rise to as much (often more) new shoot 
growth as would have arisen from the unpruned tree. This is well 
illustrated by Figs. 50 and 51 which show the response of two trees of 
Grimes to the same amount of pruning, the tree on the left having been 
headed back and that on the right having been thinned out. 



Table 11. — Influence of Heading Back and Thinning Out on Shoot and 

Spur Formation in Young Apple Trees 

(After Gardner 22 ) 






o & 

s. M., 



i> 3 

& a 



2ll 

o m S 

2 2 e 

lis 



5 HZ 

H o o 
0) M S 

S 2 c 

?X o 






O m °> 

C C 
2'" 











X 










0! 


£ 


fl 






c^ 


(1) 


tr 


a 


61 


-w 







a 




cu 


> 


j= 




n 





B«0 
3---H 



S3 t- 3 



Grimes 
Grimes 
Grimes 
Grimes 
Gano . . 
Gano. . 
Gano. . 
Gano. . 
Rome . 
Rome. 
Rome. 
Rome. 
Esopus 
Esopus 



32 


26-50 


697 


2297 


82 


23 


26-50 


731 


2495 


83 


39 


51-75 


389 


1315 


22 


36 


51-75 


368 


1362 


23 


18 


26-50 


450 


2376 


15 


14 


26-50 


462 


2609 


14 


4 


51-75 


560 


2493 


15 


10 


51-75 


562 


2435 


15 


19 


26-50 


507 


1990 


9 


17 


26-50 


508 


1956 


10 


8 


51-75 


1007 


2851 


9 


21 


51-75 


682 


2230 


8 


29 


46-76 


444 


1659 


28 


27 


46-76 


461 


1813 


28 



Thinning 

Heading 

Thinning 

Heading 

Thinning 

Heading 

Thinning 

Heading 

Thinning 

Heading 

Thinning 

Heading 

Thinning 

Heading 



4123 
5703 
2308 
3328 
4577 
6293 
5072 
5846 
3352 
3915 
4785 
4474 
2122 
4031 



360 

322 

130 

101 

158 

158 

110 

111 

43 

25 

54 

25 

180 

144 



Influence on General Shape and Habit. — Incident to quite different 
effects of heading and of thinning upon the amount of new shoot growth 
and the number of new spurs are the influences of these practices on gen- 
eral shape and growth habit. Thinning out places no check on the 
natural tendency to grow principally from the terminal and subterminal 
buds. Consequently plants pruned exclusively in this way grow tall 
and wide spreading and they gradually develop a more open, "rangy" 
habit than they would otherwise. This may be advantageous or dis- 
advantageous to the grower, depending on a number of conditions. On 
the other hand constant heading checks this tendency to extend out and 
up and results in a plant compact in habit and often very dense in growth. 
The average well kept hedge furnishes an extreme example of the direc- 
tion in which all heading tends. Indeed much of the usual pruning of 
the bramble fruits, which consists largely in heading back both leaders 
and laterals and the pruning that frequently is afforded other deciduous 
fruits — especially when they are young — results in a type of growth and 



PRUNING— THE METHOD 423 

a condition of tree in many ways closely comparable to that of the privet 
or osage orange hedge. 

Influence on Fruit-bud Formation and Fruitfulness. — The orchard 
is grown and maintained not primarily for its shoot growth or for its 
spurs, but for fruit. The grower therefore wishes to know the influence 
of different pruning practices on fruit-bud formation. It has been 
shown previously that this occurs at varying times in diverse plants 
and that different species present entirely unlike fruit bearing habits. 
That is to say, some bear on spurs, some on shoots; some bear terminally, 
some laterally. If, then, pruning practices differ greatly in their influ- 
ences on spur formation and shoot formation, corresponding, perhaps 
greater, differences may be expected in their influences on fruit-bud 
formation and fruiting. The practice that leads to greater fruitfulness 
in one species may tend in the opposite direction in another. Thus 
heading back may be a good practice in growing the peach because it 
encourages new shoot formation on which the fruit buds are borne and 
on the other hand, heading back may be a bad practice for the pear, 
because it generally limits the formation of fruit spurs on which most of 
the fruit of this species is borne. 

In contrast to thinning out, heading back generally tends not only to 
reduce the number of spurs in spur bearing species but also to lower the 
percentage that differentiate fruit buds. In these same species, thinning 
out, though it may reduce somewhat the total number of fruit spurs, has 
been shown under some conditions to lead to the formation of fruit buds 
and to the maturing of fruit on a larger percentage of those remaining. 
Data on this question obtained from pruning experiments with young 
apple trees in Oregon are furnished in Table 12. The figures presented 
in the last three columns of this table also show something of the influence 
of these two pruning practices on fruit-bud formation on shoots. Though 
the apple is not generally considered a shoot bearer, where this investiga- 
tion was carried out, two of the varieties studied, Rome and Gano, bear 
principally on shoots for the first few seasons. Thinning out generally 
encouraged terminal and lateral fruit-bud formation on shoots more 
than a corresponding heading back, though there were some exceptions. 
In commenting on these data Gardner 22 says: 

"The moderately thinned Grimes trees were somewhat more than twice as 
productive of fruit buds as the correspondingly headed trees ; the heavily thinned 
Grimes trees were 10 times as productive of fruit buds as correspondingly headed 
trees. The moderately thinned Rome trees were nearly twice and the heavily 
thinned, nearly five times as productive of fruit buds as those correspondingly 
headed. On the other hand, moderately thinned Gano trees produced but 
slightly more fruit buds than those moderately headed, and heavily thinned 
trees of this variety averaged distinctly fewer buds than those heavily headed. 
The last statement also holds true of the heavily pruned Esopus trees. A more 



424 



FUNDAMENTALS OF FRUIT PRODUCTION 



Table 12. — Influence of Thinning Out and Heading Back Shoots on Fruit- 
bud Formation in the Apple 

(After Gardner 22 ) 



W 



Grimes 

Grimes 

Grimes 

Grimes 

Grimes 

Grimes 

Gano. . 

Gano. . 

Gano . . 

Gano. . 

Rome. 

Rome. 

Rome. 

Rome. 

Rome . . 

Esopus 

Esopus 

Esopvis 



No pruning 

Thinning 

Thinning 

Heading 

Thinning 

Heading 

Thinning 

Heading 

Thinning 

Heading 

No pruning 

Thinning 

Heading 

Thinning 

Heading 

No pruning 

Thinning 

Heading 



1-25 
26-50 
26-50 
51-75 
51-75 
26-50 
26-50 
51-75 
51-75 



o SP 



"on 
^= S3 



a uid 
3 ao 



26-50 
26-50 
51-75 
51-75 



41-76 

41-76 



71 
38 
32 
23 
39 
36 
18 
14 

4 
10 
28 
19 
17 

8 
21 
27 
29 
27 



402 

457 

360 

322 

130 

101 

158 

158 

110 

111 

142 

43 

25 

54 

25 

635 

180 

144 



o o Si 



St* r*- 
3-h 
3 D.C5 



29.5 

24.8 

31.7 

8.9 

18.0 

0.1 

12.9 

14.8 

8.5 

14.6 

31.6 

5.6 

5.2 

5.0 

3.5 

41.9 

17.2 

11.4 



"S W S 



E ^ 

a o a 



2.7 
3.9 
2.6 
7.4 
0.9 
1.3 
59.3 
65.0 
43.5 
53.6 
3.5 
1 
5. 
2. 
2. 
0. 

2. 



3tc2 



5.0 

4.6 

10.0 

2.2 
6.2 
1.0 



31.6 
16.4 
15.0 
13.7 
72.4 
47.5 
21.9 
51.7 

6.4 
10.4 

7.2 
17.6 



3 o > 

•3 ^ 



37.2 
33.3 
44.3 
18.5 
25.1 
2.4 

103.8 
96.2 
67.0 
81.9 

107. 
54. 
32. 
59. 
12. 
52.6 
24.5 
31.1 



detailed study of the table brings out a number of additional points. In the 
first place, it is noted that thinning, as compared with an equally severe heading, 
almost invariably led to an increased production of fruit buds upon fruit spurs. 
The one exception to this statement is furnished by the heavily headed Gano 
tree, a variety in which severe heading of short shoots in the interior seems often 
to have the effect of forcing the development of strong fruit spurs from the remain- 
ing lateral buds. The short interior shoots of other varieties do not show such a 
tendency to respond to severe heading in this way. Heading-back was invariably 
accompanied by a greater development of terminal fruit buds on shoots than 
thinning out. In the case of a variety like Gano, that when young bears a 
large percentage of its fruit buds in this way, this effect may be sufficient to give 
the tree a larger total number of fruit buds than correspondingly thinned trees. 
Attention is called, however, to the fact that a continuation of the winter heading 
year after year would remove the fruit buds on all the shoots headed and thus 
actually result in decreased flower and fruit production as compared with thinning. 

"Another point worth noting, but not brought out in the table is the fact 
that the shoots bearing terminally average much shorter in the thinned than in 
the headed trees. They are generally so placed, moreover, that in the thinning 
of shoots they can be left to advantage while sterile ones are taken out. 

"Except for Esopus, winter thinning of shoots, as compared with heading, 
led to greatly increased production of lateral fruit buds on shoots. In the case 



PRUNING— THE METHOD 425 

of the heavily pruned Rome trees, the proportion of such lateral fruit buds was 
8 to 1 under the two pruning treatments. Furthermore, the distribution of these 
lateral fruit buds is such that a given heading-back (for instance, 50 per cent) 
would remove a much larger percentage than an equally severe thinning out. 
This percentage, in the case of Esopus, would be enough greater more than to 
counterbalance the effect upon total fruit production of larger numbers of such 
lateral fruit buds. 

"Taking all these facts into consideration, it is evident that the effect of 
thinning-out and likewise of heading back upon fruit-bud formation varies 
greatly with the variety. The pruning practice that will lead to the largest 
fruit-bud production in one variety will not necessarily lead to it in another. 
Thus it becomes important for the grower to become better acquainted with 
the exact fruiting habits of his varieties under his conditions as well as to the 
response that these varieties make to various pruning practices." 

Thinning and Heading Lead to Different Nutritive Conditions. — The 
explanation of the varying effects of thinning out and of heading back 
on fruit-bud formation is not found exclusviely in the different fruiting 
habits of the several species and varieties. New growth is made chiefly 
at the expense of stored foods, particularly carbohydrates. In the section 
on Nutrition data are presented showing that the younger wood is 
comparatively richer in food reserves than older tissues. Heading back, 
therefore, removes a larger amount of the tree reserves than a correspond- 
ingly severe thinning out and leaves it less able to recuperate, especially 
if the pruning has been severe. 

It is also pointed out in the section on Nutrition that the initiation 
of the fruitful condition, or in other words fruit-bud formation, is associ- 
ated with an accumulation of carbohydrates in the regions where fruit 
buds can be formed. Carbohydrate accumulation in turn depends on 
carbohydrate manufacture on the one hand and on carbohydrate utiliza- 
tion on the other. When the latter process lags behind the former, oppor- 
tunity is finally afforded for the laying-down of fruit buds. In the last 
analysis, therefore, pruning influences fruit -bud formation to the extent 
that it influences carbohydrate accumulation or carbohydrate utilization 
or the status of the ever changing ratio between them. 

Thinning out not only removes less stored food than a corresponding 
heading back, but, as just pointed out, it also leads to increased fruit- 
spur formation and decreased shoot growth. This means decreased 
carbohydrate utilization and increased carbohydrate manufacture, 
because spurs are short growths with relatively large leaf surfaces. Their 
growth is made very early in the season and from then on they are manu- 
facturing and accumulating rather than spending or dissipating organs. 
On the other hand heading back produces fewer of these short growths 
and more of the longer and stronger shoots that complete their growth 
much later. Consequently they more nearly exhaust the plant's re- 



426 FUNDAMENTALS OF FRUIT PRODUCTION 

serves than the shoots and spurs of thinned trees and their carbohydrate 
contributions to the tree as a whole come later and may amount to less. 

Furthermore the thinned is more open than the headed tree. Its 
leaves are better exposed to light and presumably they are for that reason 
somewhat more effective manufacturing organs. The more common 
formation of fruit buds in the better exposed parts of the tree is evidence 
on this point. The rather general production of fewer and smaller leaves 
on spurs in the interior shaded portions of compact headed trees, in 
contrast to the larger and more numerous leaves on the spurs of open 
thinned trees, is another fact pointing to material differences in the rate 
of carbohydrate accumulation in their fruiting wood. 

Still another reason for the difference in response from heading back 
and from thinning out lies in a disturbance of an equilibrium within the 
branch itself induced by heading back. Each branch, as it grows, may 
be regarded as a system in equilibrium, comparable to that in the plant 
as a whole. That is, there is a balance between part and part. If a 
portion of the branch is removed this balance is disturbed. Equilibrium 
is reestablished by regeneration of the part pruned away. Apparently 
little readjustment is necessary after thinning out, because the equilib- 
rium of the remaining branches is not disturbed. The adjoining parts 
will function more nearly as they would, had no pruning been done. 

The Places of Thinning and of Heading in Pruning Practice. — The 
preceding discussion shows that no rules can be laid down as to the relative 
amounts of heading and of thinning that should be given trees of a certain 
kind or of a certain age. Rather is it necessary to study carefully each 
problem as it arises, to interpret and to apply the general principles that 
have been pointed out. In a general way, however, it may be stated that 
both the development of a more extensive fruiting system and more 
especially the better and more efficient functioning of that system are 
favored more by thinning than by heading. There are notable instances 
of other effects, however, e.g. in the bramble fruits, in which the heading 
back of the canes or other growth limits the energies of the plant to pro- 
duction on the remaining shoots or spurs and causes them to produce 
larger, if not more, fruits. In the section on Fruit Setting it is pointed 
out that pinching back the growing shoots of the grape before blossoming 
sometimes leads to a better setting. In most species continued thinning 
out leads eventually to tall or wide spreading and "rangy" plants, plants 
that require wider spacing in the orchard, that often make undue expense 
in pruning, spraying and other care and that are unable to mature their 
crops without a great number of mechanical supports. Judicious heading 
back corrects these tendencies and promotes a compact type of growth 
that, in these respects, is much more satisfactory. In fact it may be 
stated that in general the main purpose of heading back is to control the 
form of the tree, bush or vine — to train it. In practice this means that 



PRUNING— THE METHOD 427 

while the trees are young they should receive relatively more heading back 
and less thinning out, because they are then being trained. As they 
grow older they should receive relatively less heading and more thinning, 
because they will require less and less training for shape and more atten- 
tion to the proper functioning of their fruit-producing wood. Species like 
the peach and grape, which, because of their growing habits, continually 
require considerable training for compactness and shape, should receive 
correspondingly more heading when mature than certain other species 
like the apple or walnut that have entirely different growing habits. 

Fine, as Compared with Bulk Pruning. — In pruning practice and in the 
consideration of pruning problems aside from those dealing with the heal- 
ing of wounds, priming is generally regarded as something directly affect- 
ing the tree as a whole. It is common to speak of pruning this tree heavily 
and that one lightly, of heading back one and thinning out another, of 
winter pruning in one instance and summer pruning in another. A certain 
tree having been neglected for a number of years is said to require a heavy 
pruning to bring it back to a vigorous productive condition. Such 
sweeping statements disregard frequent cases in which though possibly 
certain parts of the tree should be pruned heavily, certain other parts 
should be pruned lightly, if at all. If a heavily pruned tree fails to attain 
quickly a vigorous productive condition there is query why the result has 
not been satisfactory. When it is decided that another tree requires 
only a light pruning, only a very few branches are removed. If such 
pruning is attended by some of the results usually accompanying heavy 
pruning there is speculation regarding the reason. These statements, 
which will be recognized as based upon very general experience, show that 
pruning is regarded somewhat as a bulk problem — as something which 
is decided on for the tree as a whole, done to the tree as a whole and to 
which the tree as a whole responds. Yet the results frequently obtained 
indicate nothing more clearly than that pruning is not exactly a problem 
of bulk. 

Results Following "Dehorning." — The sucker type of growth that 
almost invariably follows very severe cutting back or "dehorning" is 
well known. If the dehorning has been done in winter or early spring, 
numerous comparatively upright shoots are produced during the following 
summer. The usual practice is to thin these out and head back those 
that are left, in order to develop as quickly as possible new fruiting 
branches. Thus is the tree "rejuvenated." So well is this procedure 
understood that the question as to when and how to rejuvenate trees has 
been considered practically settled. However, even a cursory examination 
of a tree that has recently received such a treatment shows that only a 
part has responded. Undisturbed branches in the lower part of the 
dehorned tree usually continue to grow in the ordinary way. Their 
spurs bear flowers and fruit but little more regularly and yield a product 



428 



FUNDAMENTALS OF FRUIT PRODUCTION 



of but little better grade than before. There is nearly the same tendency 
for their older spurs and smaller fruiting branches to become gradually 
weaker and die. Apparently neither as whole units nor in their separate 
parts have these lower branches been accelerated or retarded in growth. 
In many cases they do not even produce watersprouts, such as develop so 
abundantly on the dehorned branches above them. In other words, an 







Fig. 52. — A Bartlett pear tree, three years after a heading back of the main upright 
limbs. Notice that the response to this pruning has been principally close to where the 
cuts were made. 



important — often the most important — portion of the tree, apparently 
has not been affected in any way by the dehorning. This is brought out 
clearly in Fig. 52. The treatment has resulted merely in the production 
of new wood to replace a portion of the old top. 

Even more striking evidence on this question of the distance to which 
the influence of pruning extends is furnished by trees that have been 
partly dehorned, that is, have had a portion of their branches cut back 



PRUNING— THE METHOD 



429 



very severely and others of equal size and reaching to an equal height 
left untouched. In such instances those responses, commonly regarded 
as characteristic of dehorning, usually are limited to the branches that 
have been cut back. These branches produce watersprouts in abun- 
dance, but the unpruned branch continues to grow and function as though 
nothing had been done to upset the usual conditions in the tree. 




Fig. 53. — An old Italian prune tree. All of the main limbs but one were cut back four 
years before this picture was taken. The unheaded limb in the center shows little response 
to the pruning. 

Examples of this occur in old trees of many species that are being top- 
worked, when the process is being distributed over a period of several 
years. The influence of the heavy pruning, incident to the top working 
process, usually is not reflected to any appreciable extent in a changed 
manner of growth in the ungrafted limbs (see Fig. 53). 

Results Attending the Removal of a Few Large Limbs. — The entire 
removal of one or more comparatively large limbs, the majority being 
left unpruned, is a type of pruning in more or less shajp contrast to the 
bulk heading back just discussed. It may be considered a kind of bulk 
thinning. Many fruit growers prune in this manner, which possesses 



430 FUNDAMENTALS OF FRUIT PRODUCTION 

at least the advantage of requiring little labor. Experience shows that 
when a single large limb is removed from almost any part of a tree, water- 
sprouts develop to take its place and the rest of the top continues to grow 
as before. The watersprouts arise, for the most part, not from limbs far 
removed from the pruning wound, but close to the point where the cut 
was made. There is an unmistakable response to the pruning, but that 
response is evident within a very limited area. The tree as a whole does 
not show it. 

Those who, after permitting a leader to develop for a number of years 
and to form a close centered tree, have finally tried to train to an open 
center or vase shape can furnish abundant evidence on the question under 
discussion. The removal of the central leader from trees of this kind 
(bulk heading back or bulk thinning out, depending on the form of the 
tree and where the cut is made), is almost always followed by the pro- 
duction of a number of watersprouts that tend to take its place. The 
subsequent removal of these watersprouts is followed by the production 
of still others, nearly always at points near the wound left by the removal 
of the leader. The unpruned branches seem little influenced by the 
cutting out of the leader. 

In attempting to train young Yellow Newtown apple or Bartlett or 
Anjou pear trees to an open center, or the Mcintosh apple or Winter 
Nelis pear to a closed center, there is difficulty in keeping these trees 
from growing dense in the center in the first instance and from spreading 
out or even growing down in the second, though the shoots are cut out or 
off. Furthermore — a matter of equal or greater importance — there is 
difficulty in making the other shoots and limbs of these same trees spread 
out or grow upright, as the case may be and thus profit by the nutrient 
materials that it is desired to divert from the closely pruned parts. In 
fact so persistently do the watersprouts tend to replace removed limbs, 
that the easiest way to develop an open centered tree is not to cut out all 
of the growth in the center, but rather to suppress it by pruning it a little 
more severely than the surrounding branches that are desired for the 
main framework. Even then it is doubtful if the usual characteristic 
growth of the remaining branches is materially changed. Similarly, when 
young trees are lightly, or even heavily, headed back new shoots are sent 
out, but mainly from points where some of them can easily replace the 
portion removed. It is not common for distant untouched portions of the 
tree to show a well defined response to pruning. 

Results Attending Spur Pruning. — As they become older, some 
varieties of apple and pear trees develop large numbers of fruit spurs, 
which often branch and rebranch until they become fruit spur clusters. 
Usually when there are such large numbers of fruit spurs only a com- 
paratively small percentage can flower and fruit in any single season and 
the record of any single spur, or even spur cluster, especially in an older 



PRUNING— THE METHOD 431 

part of the tree, would show very irregular fruiting. In such trees, 
though there is little vegetative growth in the general acceptation of the 
term, nearly all the energies of the tree are really being absorbed in a 
slow vegetative growth of the spurs. The recognition of this condition 
leads the grower to try dehorning or some other type of bulk pruning as a 
remedial measure. That bulk pruning is only a partial remedy has 
already been shown. Occasionally a grower tries the removal of a part 
of the spurs from such trees. As the spurs possess a very large percentage 
of the growing points and bear practically all of the leaf system of a tree 
in such condition, a thinning of spurs is in one sense the equivalent of a 
heavy pruning though the total weight of the wood removed may be 
negligible. When treated in this way trees produce few or no water- 
sprouts, though the removal of a few large branches with an equivalent 
number of growing points leads to their formation. However, the re- 
maining spurs grow more vigorously and the new shoots developing from 
lateral and terminal buds are much larger and stronger. As a net result 
though the tree is changed little, if at all, in general form, the rate of 
growth of nearly all its individual parts is accelerated and the ways in 
which they function are materially changed. The tree as a whole has 
been affected because nearly all its individual parts have been affected. 
Application to Practice. — A consideration of the points that have been 
made leads unmistakably to at least one conclusion: namely, that the 
radius of influence within the tree of any pruning (that is, the cutting 
out or cutting back of any particular shoot or branch) is comparatively 
small. Parts close to the pruning wound, or perhaps close to a space 
left by the removal of a branch, respond to the pruning treatment. Gen- 
erally speaking, other parts of the tree do not. In other words, pruning 
does not appreciably affect the tree as an entity ; it affects the whole tree 
only indirectly through its effect on limited portions. To stimulate the 
formation of fruit spurs pruning must be done close to the point where 
they are desired and to increase the productivity of spurs already present 
pruning must be done in their immediate neighborhood. This in turn 
means light, or rather fine, as opposed to coarse, pruning. It is neces- 
sary to avoid bulk pruning and give greater attention to detail. Theoret- 
ically pruning should concern itself mainly with shoots, spurs and the 
smaller branches rather than with older and larger wood. Practically 
some exceptions must be made, particularly in trees that have been 
neglected for several years, because the operation must be conducted with 
due regard to economy. The finer and the more evenly distributed the 
pruning the more expensive it is and the net returns become subject to 
the law of diminishing returns. Therefore in practice the most profitable 
kind of pruning is always a compromise between the type which is best 
for the tree and the type which can be done most cheaply. 

Most of the trouble from fungous or bacterial infection comes from 



432 FUNDAMENTALS OF FRUIT PRODUCTION 

the large wounds, those made in bulk pruning. This is not an important 
factor in the culture of the bush or vine fruits but it is usually of consider- 
able importance in the tree fruit plantation. Indeed it is not too much 
to say that the life of the average orchard tree is reduced by one-third 
through the work of wound fungi and bacteria. Fine, as opposed to 
coarse or bulk, pruning is the most practicable way of preventing losses 
of this sort. 

Carrying the line of reasoning a step further it becomes evident that 
pruning should be regular and frequent. This is a statement which most 
growers know to be true from observation and experience, though the 
reasons may not always be clearly understood. However, the points 
that have been brought out furnish an explanation of some of the charac- 
teristic results following irregular pruning. Trees left unpruned for 
several years usually seem to require the removal of some of the larger 
branches or limbs. This approaches the bulk type of pruning and stimu- 
lates new vegetative growth more than it invigorates the older fruiting 
wood; new vegetative growth of this sort is as likely to increase as to 
diminish difficulties. 

What has been stated should not be construed as condemnation of 
occasional heavy pruning, that is, the removal of a considerable amount 
of growth. Though heavy pruning as commonly done is bulk pruning, 
it is not necessarily so. It may consist in the removal of a large amount 
of shoot growth and small branches and instead of giving rise to water- 
sprouts, it may stimulate the normal vegetative growth and the fruit 
spur system. The spur pruning to which reference has been made is 
evidence to this effect. 

Even bulk pruning is not always harmful. There are occasions when 
a growth of strong vigorous shoots or watersprouts is desired in some part 
of the tree. Particularly is this true in trees that have suffered from win- 
ter injury or some other form of dieback. Then too, it should be remem- 
bered that many species do not bear on fruit spurs or on short growths of 
any other kind. Their flower buds are formed freely upon their longest 
and strongest shoots and bulk pruning which leads to this type of vege- 
tative growth may increase rather than check fruitfulness. 

Root Pruning. — Root pruning has long been a recognized practice 
among many European fruit growers, particularly those of the British 
Isles and the adjacent continental countries and for many years it was 
generally recommended (but rarely done) in the United States. Though 
its use has not been limited to trees grown as dwarfs it has been employed 
much less commonly with standards. In this country particularly, as the 
culture of dwarf fruit trees has become relatively less important, root 
pruning has all but disappeared from the list of cultural operations. 
However, a certain amount of root pruning is almost always accomplished 
in the regular cultivation of standard orchard trees. For this reason, 



PRUNING— THE METHOD 433 

though tillage is thought to effect a root pruning seldom, some of the 
more important effects of severing a portion of the tree's roots at different 
seasons may well be noted. 

In the culture of dwarf trees of almost any kind, Rivers, 42 one of the 
leading exponents of the practice, recommended an annual, or at least a 
biennial, shortening of all the roots. In describing the operation he said : 
"Open a circular trench 18 inches deep around the tree, 18 inches from 
the stem, and cut off every root and fibre with a sharp knife. When 
the roots are so pruned, introduce a spade under one side of the tree, and 
heave it over so as not to leave a single tap-root; fill in your mould, give a 
top dressing of manure, and it is finished. The diameter of your circular 
trench must be slowly increased as years roll on; for you must, each year, 
prune to within 1^ or 2 inches of the stumps of the former year. Your 
circular mass of fibrous roots will thus slowly increase, your tree will 
make short and well-ripened shoots, and bear abundantly." It is gen- 
erally recommended that this root pruning be done in the late fall. The 
major repsonse will then be evident the following spring and summer in a 
reduced vegetative growth and an increased formation of fruit buds. 

Some conception of the dwarfing influence of continued root pruning 
on apples grown on Paradise stocks is afforded by an investigation con- 
ducted at the Woburn Experiment Station in England. In summa- 
rizing their results, Bedford and Pickering 5 state: "In one series the 
trees were root-pruned every year, in another every other year, and in 
a third every fourth year; actual lifting from the ground being adopted, 
till they became too large for this to be done without excessive injury. 
The check caused to the growth of the trees was apparent from every 
point of view, and its extent may be gathered from the weights of the 
trees when they were ultimately removed. Thus with the Cox, which 
were removed after 15 years, the weights of those trees which had been 
root-pruned every fourth year were only 43 per cent of those which had 
not been root-pruned; where the operation had been performed every 
other year, the weights were 7 per cent of the non-treated trees, 
and with the yearly operation, 3 per cent; indeed, in the last case, the 
trees had scarcely increased in weight since they had been planted, and 
had been dead for several years before they were removed." These 
investigators then state that root pruning is followed by increased crop 
production, though usually this is not evident until the second season 
after the operation. However, repeated root pruning so weakens the 
trees that they soon fall behind non-treated trees in yield. Bedford 
and Pickering conclude that "root-pruning is an operation which should 
be practiced with extreme moderation, and only in those cases where 
excessive branch-growth calls for stringent measures. " The root 
pruning investigations of Drinkard 18 in Virginia led to practically the 
same conclusions. He reported a greatly reduced shoot growth, with 

28 



434 FUNDAMENTALS OF FRUIT PRODUCTION 

leaf areas on the root pruned trees only 5 to 20 per cent of those on the 
checks. Furthermore the leaves of the treated trees were smaller and 
paler than those of the untreated trees. This check in vegetative 
growth was accompanied by an increased formation of fruit buds; these, 
however, were so weak that comparatively few set fruit and yields were 
less than those obtained from trees not root pruned. 

The experimental results of these and of other recent investigators 
do not, on the surface, agree with the opinions of many of the earlier 
writers regarding the desirability of root pruning. The quotation 
from Rivers, however, included with the recommendations for annual 
or biennial root pruning one for liberal applications of manure and a 
study of the earlier literature dealing with this subject shows that arti- 
ficial feeding and often artificial watering was assumed for practically 
all root pruned trees. The relatively great productivity of the root 
pruned dwarfs of European and other gardens therefore should be re- 
garded as due only partly to root pruning, some of the other attendant 
practices being perhaps more responsible. 

Seldom, if ever, would the operations incident to clean culture or 
any other system of soil management result in a root pruning as severe 
as that contemplated in the regular practice that goes by that name. 
Nevertheless the deep plowing of trees growing in a shallow soil or in 
a soil that compels shallow rooting actually effects a considerable, and 
occasionally a very severe, root pruning. This may be expected to 
afford a temporary stimulus to fruit-bud production and at the same time 
to check vegetative growth more or less, though either or both of these 
direct effects may be masked by the indirect influence that the tillage 
exerts. 

Special Pruning Practices. — Stripping, notching, ringing and girdling 
may be considered together as a group of special orchard practices rather 
ciosely related to pruning. The names used to designate them are suffi- 
ciently descriptive to make unnecessary any further explanation of the 
procedure involved. They are all performed with the aim of so control- 
ling the translocation of elaborated foods that their accumulation in 
certain parts may lead to increased fruit-bud formation and hence to 
greater fruitfulness or to a better setting of the flowers or to a better 
development of the fruit itself. 

The upward movement of water in the tree, of the transpiration stream, 
is commonly thought to occur in the outer layers of the wood. Knowl- 
edge of the translocation of elaborated foods is rather fragmentary, 
though it is rather generally agreed that their downward movement 
is through the phloem. Recent investigations of Curtis 14 indicate that 
no appreciable quantities of carbohydrates move upward through the 
xylem and that such elaborated food materials as are stored in the xylem 
move only radially in the wood. Their upward transfer is limited mainly 



PRUNING—THE METHOD 435 

to the tissues of the bark, except for a limited translocation by means of 
diffusion. Consequently those portions of shoots or branches above the 
point where the flow of elaborated foods has been checked by girdling 
or ringing depend on their own resources in so far as elaborated foods 
are concerned. That is, they cannot receive foods manufactured else- 
where in the plant and foods that they manufacture must be stored 
within their tissues or utilized by them. If the operation is performed 
during the dormant season or very early during the growing season, 
vegetative growth above the ringed or girdled point will be checked 
because of the early exhaustion of the stored carbohydrates and the 
reduced leaf area will limit the synthesis of a new supply. On the other 
hand, this new supply that is synthesized cannot be translocated to 
the roots or other parts of the tree and must be stored or utilized in 
close proximity to its point of manufacture. Girdling or ringing after 
the first flush would permit a greater amount of growth beyond the 
point of operation because food stored elsewhere would be to some extent 
available for this new growth and following the ringing there would be 
opportunity for a correspondingly greater accumulation of foods. The 
general influence of notching and stripping is in the same direction as 
that of ringing, but is less pronounced because the operations themselves 
only partly stop translocation through the phloem. 

It is evident that the effect of any of these special practices on 
accumulation and concentration of food materials is almost certain to 
be more pronounced in the summer than it is during the spring months. 
This explains why they so often fail to encourage the formation of fruit 
buds and greater fruitfulness for which they have been so frequently 
recommended, the period of fruit-bud differentiation having passed before 
their concentrating effects are realized. 

The following quotation from Drinkard's 18 summary of his work in Virginia 
bears on this point: "Ringing at different seasons when accompanied by or 
preceded by spring pruning, of the branches produced no noticeable stimulation 
of fruit bud formation. Ringing at the time growth was resumed in the absence 
of spring pruning did not stimulate fruit bud formation. The treatment was 
given too early. Ringing at the time the foliage was fully developed in the 
absence of spring pruning gave the best results; however, when the treatment was 
given at the time the fruit buds began to become differentiated there was some 
stimulation to fruit bud development. Stripping at different seasons when 
accompanied by or preceded by spring pruning, had no stimulative effect on 
fruit bud formation. The effects of stripping were offset by those of spring 
pruning. Stripping at the three seasons already mentioned, in the absence of 
spring pruning, stimulated fruit bud formation uniformly." 

The facts relating to food translocation and manufacture may also 
partly explain why ringing so frequently results in an increase in size or 
in some modifications of the texture or composition of the fruit that 



436 FUNDAMENTALS OF FRUIT PRODUCTION 

matures during late summer or in early fall. Thus Daniel 15 reports 
a marked increase in size of the fruits of the tomato and egg-plant from 
ringing; Paddock, 35 Bioletti 6 and Husman 29 have reported a similar 
increase in grapes. On the other hand Howe 28 found no increase in 
size of fruit in ringed apples, pears, cherries and plums, though he reports 
other late-season effects in the earlier maturity of fruit and a much 
earlier dropping of the foliage Paddock 35 likewise has reported an 
earlier maturity of grapes borne on ringed shoots, an earliness sometimes 
amounting to as much as two weeks. It has been noted frequently 
that grapes borne on ringed shoots contain relatively less sugar and more 
acid 29 or are somewhat poorer in quality 35 than those borne on untreated 
shoots. 

In the section on Fruit Setting ringed shoots of the grape and of 
certain other fruits are mentioned as setting in many cases a larger per- 
centage of their blossoms than those not treated in this way, if the opera- 
tion is performed just previous to the opening of the flowers. Seldom is 
the difference great enough to make the operation worth while for this 
purpose. A few varieties of the grape, however, without such treatment 
grow so vigorously that they set but little fruit and with them the opera- 
tion should be performed annually. Thus in the Fresno (California) 
Experiment Vineyard 12-year-old ringed Panariti grafts on 10 different 
resistant stocks averaged 7.5 tons per acre during 1917 and 1918, while 
unringed vines on the same stocks and under the same conditions aver- 
aged 2.3 tons per acre. 29 

From the data presented here and in the section on Nutrition it 
is evident that the concentrating influence of ringing, stripping and 
related practices depends not alone on their effects on new vegetative 
growth, leaf area and food manufacture, but also on food utilization. 
In turn the utilization of the elaborated foods that are synthesized in the 
shoot beyond the point of ringing depends on the available water and 
nutrient supply. If the soil is comparatively dry and low in nitrates, the 
effect of ringing or related practices may be quite different than with an 
abundant supply of both moisture and nutrients, because the products 
of synthesis beyond the ringed point may be utilized in an entirely 
different manner. This factor has received very little consideration and 
it must be properly evaluated before any ringing operation can be per- 
formed with certainty of its effects on either fruit bud formation or on the 
development of fruit. Inadequate consideration of this factor has caused 
much apparent contradiction and uncertainty in the results attending this 
group of practices. 

In at least one respect there is general agreement among those who have 
employed ringing, stripping or other operations to check the transfer of 
food. They all report a tendency to check the growth of the plant during 
later years and thus have a dwarfing influence. This is proportional to 



PRUNING— THE METHOD 437 

the degree of starvation of the roots through separation from their supply 
of elaborated foods and its ultimate effect on growth and development is 
in every way comparable to the results attending root pruning. It 
should be mentioned also that ringing inflicts mechanical injuries that 
sometimes heal slowly and for this reason alone it should be used with 
great caution, if at all, on certain fruits like the plum and cherry. Appar- 
ently with the grape alone, among the common deciduous fruits, should 
this group of practices be a regular cultural treatment and even in the 
grape only a very few of the most vigorously growing varieties can be 
ringed with profit. Other cultural treatments may be combined and 
employed to better advantage to bring about the same conditions that 
these special practices induce and with far less danger of undesirable 
after-effects. 

Summary. — In kind all top pruning may be considered either as 
heading back or as thinning out. These two kinds produce quite differ- 
ent results, particularly as the pruning increases in severity. In general, 
thinning out is accompanied by less new shoot growth but more new spur 
and fruit-bud formation than correspondingly severe heading back. 
Heading back tends to make trees more, and thinning out less, compact 
in habit. The different responses from the two methods of pruning are 
due probably in large part to the distinct nutritive conditions to which 
the practices give rise. Both methods have their places in orchard man- 
agement, heading back being more useful in keeping the tree well shaped 
and thinning out in developing its fruiting wood and in keeping that wood 
in good working order. As most trees grow older they should receive 
relatively more thinning out and less heading back. 

In kind, pruning may be coarse or fine with essential differences 
in the attendant responses. Coarse or bulk pruning tends to disturb 
seriously the equilibrium within the plant and generally results in the 
production of watersprouts. Careful fine pruning, on the other hand, 
evokes a much more general response. The ideal pruning is fine, as 
opposed to coarse or bulk; however in practice a compromise must gen- 
erally be made between the kind which is best for the tree and the kind 
which is most economical. 

Root pruning has a dwarfing influence and its greatest use is in the 
culture of dwarf trees. The supposed influence of root pruning in pro- 
moting fruitfulness is due probably in part, if not largely, to other prac- 
tices such as irrigation and fertilization which generally accompany the 
culture of dwarfs. 

Girdling, notching, ringing and stripping are special practices, related 
to pruning, which have for their object the promotion of fruitfulness 
through interrupting the translocation of foods. Their use is attended 
by uncertain results and they are not to be recommended under average 
conditions. 



CHAPTER XXIV 

PRUNING— THE SEASON 

The subject of pruning has been shown to present three major aspects, 
one of which is a consideration of the varying response from pruning at 
different seasons. Theoretically at least this involves a study of the 
different effects from pruning each successive month, or perhaps at more 
frequent intervals. Practically the question is much less complicated, 
involving principally a comparison of the effects attending pruning during 
the growing season with those following winter pruning. 

Pruning at Different Times During the Dormant Season. — Prun- 
ing at different times during the dormant period may, however, re- 
ceive brief consideration. Dormant or winter pruning is generally 
understood to mean late winter or early spring pruning, since it is usually 
done then. Winter pruning, however, may begin as soon as the plants 
become more or less dormant in the fall and may continue into the spring 
until vegetation is starting actively. The supposed advantages and 
disadvantages of pruning at different times during the dormant period 
have been long discussed. Apparently so far as any effect on the amount 
and character of subsequent growth is concerned there is little or no 
difference. This is brought out clearly by experimental work with apples 
in England 4 and in Minnesota 8 and with grapes in New York. 24 On the 
other hand since there is a gradual translocation of food materials from the 
canes to the trunk and roots of the grape during a 3- or 4-weeks period 
following leaf fall, 48 pruning before this translocation is complete or after 
the reverse movement has begun in the spring should result in a some- 
what greater check to vigorous growth of the vine than a corresponding 
pruning during the period between these extremes. This effect has 
been noted both in France 40 and in California. 6 

In California the time of winter pruning has been found to be impor- 
tant in determining when grape vines of the Vinifera group start growth. 
Vines pruned immediately after the fall of the leaves started earliest; 
those pruned in midwinter started about 4 days later and those pruned 
considerably later, when bleeding commenced, were delayed about 6 days. 
"Pruning when the terminal buds commenced to swell retarded the 
lower buds 11 days, and, when the terminal buds had grown 2 or 3 inches, 
20 days." 6 In other words the lateness of starting of the buds was in 
the order of the lateness of the priming. 

In commenting on some of the practical applications of these facts in grape 
culture in California Bioletti 6 remarks: "The retardation of the starting of the 

438 



PRUNING— THE SEASON 439 

shoots in the spring may be a valuable means of escaping the injurious effects of 
spring frosts. In one of our tests, the crop on nine rows pruned Mar. 13, was 
saved, while that of 12 rows pruned Nov. 19, and Dec. 21, was completely 
ruined by a frost on Apr. 21. Late pruning also retards the blossoming though 
somewhat less than it does the starting. Pruning as late as March may retard 
the blossoming 10 days. The time of ripening is also influenced slightly in the 
same direction. When spring frosts occur, this influence appears to be reversed. 
The vines pruned early may blossom and ripen their fruit later. This is because 
the frost having destroyed the first shoots, the only flowers and fruit which 
appear are on buds which have started after the frost . . . 

"Pruning may be done, therefore, in frostless locations and with varieties 
which set their fruit well, at any time when the vines are without leaves. Where 
spring frosts are common the pruning should be as near the time of the swelling 
of the buds as possible. The benefits of late pruning without its inconveniences 
can be obtained by the system of 'double' or (clean) pruning practiced in some 
regions. This may be applied in various ways. The simplest is to shear off all 
the canes to a length of 15 to 18 inches at any time during the winter that is 
convenient. This permits plowing and other cultural operations, and the final 
pruning is done in April. A better method is to prune the vine as usual but to 
leave the spurs with four or five extra buds. These spurs we then shortened 
back to the proper length as late as practicable. In some cases the method 
practiced in the Medoc may be used. This consists in leaving a foot or 15 inches 
of cane beyond the last bud needed and removing all the extra buds at the time 
of pruning. The base buds are said to be retarded by the length of cane above 
them the presence of buds on the cane having no effect." 

Pruning late in the dormant season is quite likely to be attended by 
more or less bleeding. Seldom is the amount great enough to be harm- 
ful though many growers prefer to avoid any. In a few species, 
as for example, the English walnut, late pruned trees may bleed very 
profusely and the moist exposed surfaces offer an excellent opportunity 
for infection. For this reason, if for no other, fall pruning may occa- 
sionally be preferable to spring priming. 

Summer Pruning. — In the discussion of the effects attending various 
amounts of winter pruning there was shown to be a slower net increase in 
size with pruned than with unpruned trees and the more severe pruning 
was shown to have the more pronounced retarding influence. Similar 
results generally follow summer pruning and for about the same reasons. 
The real question is whether or not summer pruning has a greater retard- 
ing effect than a correspondingly severe winter pruning of the same kind. 

Influence on Vegetative Growth. — The new shoots and leaves in the 
spring are built chiefly at the expense of food materials formed the 
preceding season and stored through the winter. After the leaves are 
fully expanded they become manufacturing organs and eventually return 
to the plant a supply of elaborated foods equal to or in excess of that 
consumed in their development. At first, however, their growth is 



440 



FUNDAMENTALS OF FRUIT PRODUCTION 



in effect parasitic and it is not until they have been active for some time 
that they have fully replaced the materials used in their growth. Sum- 
mer pruning removes them after they have levied their tax on the 
tree's reserve foods and often before they have contributed much to its 
welfare. It must have, generally, a greater retarding influence on net 
increase in size than a correspondingly heavy winter pruning. This 
devitalizing effect of summer pruning has been noted by many observers 
and recently has been the subject of a number of experimental studies. 
Alderman and Auchter 1 found that young summer pruned apple trees 
averaged only 120 feet of new shoot growth in 1915 while winter pruned 
trees of the same age and of the same varieties averaged 188 to 216, 
according to the severity of the pruning. The summer pruned trees 
increased in spread, height and circumference more rapidly than trees 
pruned very severely in the winter, but much less rapidly than those 
pruned moderately or lightly in the winter. Apple trees just coming into 
bearing produced, after winter pruning, shoots that were 20 to 50 per 
cent longer and 10 to 20 per cent thicker than those on summer pruned 
trees. In one orchard under investigation they found that the total leaf 
area of summer pruned trees averaged only from 299 to 459 square feet, 
that of trees pruned both summer and winter averaged from 527 to 794 
square feet and that of trees pruned only during the winter averaged 
from 660 to 1144 square feet. Not only were there fewer leaves on the 
summer pruned trees, but these leaves averaged smaller in size. The 
leaves of the summer pruned trees were paler and yellowish, suggesting 
an additional reduction in their photosynthetic abilities. Arkansas and 
York Imperial trees in full bearing, on the other hand, showed practically 
no difference in the responses to summer and to winter pruning. In 
fact the summer pruned trees of middle age produced more terminal 
shoot growth than those pruned lightly during the dormant season, 
though somewhat less than those pruned heavily. Table 13 presents 
data obtained in England from pruning back weak declining plum trees at 
various seasons. The figures show the relative lengths of the new 
shoot growth. In this case the July pruning was little short of disastrous 
to the trees. Certain experimental results obtained in Virginia from 
various summer and winter prunings combined with special practices 

Table 13. — Relative Length of New Shoots of the Plum, Cut Back at 

Different Dates 

{After Bedford and Pickering*) 



May 27 


July 14 


Nov. 2 


Mar. 16 


May 15 


July 14 


Not cut 
back 


1905 


1905 


1905 


1906 


1906 


1906 




125 


75 


100 100 


65 


18 67 



PRUNING— THE SEASON 



441 



such as ringing, stripping and root pruning, show, despite some apparent 
inconsistencies, that pruning during the growing season checks new shoot 
formation and increment in trunk circumference more than does winter 
pruning. 19 Batchelor and Goodspeed, 3 reporting an experiment with 
young bearing Jonathan and Gano apple trees in Utah, state that summer 
pruning caused reduced vitality, though their figures show that the 
average length of the new shoots under both pruning treatments was 
practically the same during the 3 years for which the data are given. 
Summer pruning, however, does not always retard growth more than 
winter pruning. Experiments in New Jersey showed that peach trees 

Table 14. — Influence of Early Summer Pruning on Shoot Development 

in Young Ap.ple Trees 
{After Gardner- 1 ) 



Variety 



Pruning treatment 



Average 
shoot 
growth re- 
moved by 
winter 
pruning, 
centimeters 



Average 
shoot 
growth re- 
moved by 
summer 
pruning, 
centimeters 



Average 

total 

shoot 

growth for 

season, 
centimeters 



Average 

net gain of 

tree in 

shoot 

length for 

season, 
centimeters 



Wagener 


Winter pruned only 


538 




2690 


2152 


Wagener 


Winter and sum- 












mer pruned 


533 


1611 


4250 


2106 


Yellow Newtown 


Unpruned 






2720 


2720 


Yellow Newtown 


Winter pruned only 


826 




3460 


2634 


Yellow Newtwon 


Winter and sum- 












mer pruned 


488 


1904 


4930 


2548 


Jonathan 


Unpruned 






3576 


3576 


Jonathan 


Winter pruned only 


967 




5165 


4198 


Jonathan 


Winter and sum- 












mer pruned 


941 


3837 


7430 


2652 


Grimes 


Unpruned 






2270 


2770 


Grimes 


Winter pruned only 


988 




2965 


1977 


Grimes 


Winter and sum- 












mer pruned 


501 


1603 


4360 


2256 



pruned during the dormant season averaged 3,821 inches of new shoot 
growth in 1916, while those pruned in the summer averaged 4,227. 7 
Though this difference is perhaps not much above experimental error, 
it at least indicates that summer pruning does not always have a dwarfing 
influence. In Table 14 are presented data obtained in Oregon showing 
the influence on shoot development in young apples of rather severe 
early summer pruning. In kind and in severity the summer pruning 
treatment was practically identical with that given in the winter. In 
every instance the summer pruned trees produced more total shoot 



442 FUNDAMENTALS OF FRUIT PRODUCTION 

growth — 58 per cent, in the Wagener trees, 44 per cent, in Yellow Newtown, 
44 per cent, in Jonathan and 47 per cent, in Grimes — than those that 
were pruned during the dormant season only. A part of this increased 
growth came before the time of summer pruning (about July 1), but the 
larger part of it was produced during the summer months following the 
pruning. The growth produced before the time of summer pruning is to 
be regarded as the consequence of a summer pruning treatment of the same 
kind the preceding season; the growth after the pruning was a direct 
response to that pruning. There was practically no difference between 
the summer and winter pruned trees in their net increase in size, except 
in Jonathan. The winter pruned trees of that variety showed a greater 
net growth, principally on account of the great amount of wood removed by 
the summer treatment. Vincent 49 in Idaho has reported the 11-year 
record of an apple orchard of Jonathan, Rome, Grimes and Wagener a 
part of which received only winter pruning from the start while the other 
part received only summer pruning (Aug. 6 to Sept. 6). In kind and 
amount the pruning of the two portions was as nearly as possible. Table 
15 summarizes some of the growth records of these trees. For the most 
part the average heights, widths and trunk circumferences were slightly 
greater in the winter pruned than in the summer pruned trees, while the 
reverse was true in regard to average shoot lengths. In no case, how- 
ever, were the differences large enough to be significant. Clearly, 
summer pruning exerted no dwarfing influence in this orchard. 

These almost diametrically opposite results attending summer pruning 
in carefully controlled experimental work can be harmonized. The 
tree is to be regarded as a system in mobile equilibrium. This equili- 
brium involves a condition of balance between part and part and between 
constituent and constituent within the plant and a condition of adjust- 
ment to the environment without. Chief among these factors of environ- 
ment are temperature, light, moisture and food supply. Growth of any 
kind is a response to the condition of the equilibrium within and of 
the adjustment without. Pruning, at any time — and more especially 
summer pruning — disturbs both the adjustment to the environment 
without and the balance within. The immediate effect on the tree as a 
whole of any summer pruning is to reduce the carbohydrate supply 
and the rate of carbohydrate manufacture and at the same time to 
increase the supply of water and other nutrients, particularly nitrates, 
that is available to the rest of the plant. The size or amount of this 
influence depends on: (1) the severity, (2) the kind and (3) the time of 
the pruning and on (4) the moisture and (5) the nutrient supply available 
in the soil. Its general effect on growth therefore may be expected to 
correspond closely to that of fertilization and irrigation at that particular 
time. If the pruning is not severe enough to reduce carbohydrate sup- 
ply and carbohydrate manufacture to the point where they limit new 



PRUNING— THE SEASON 



443 



Table 15. — Growth Records of Summer and Winter-pruned Apple Trees in 

Idaho 

(After Vincent 49 ) 



Variety 


Pruning 


Average 

shoot 

length 

eleventh 

year, inches 


Average 

height 

eleventh 

year, feet 


Average 

width 
eleventh 
year, feet 


Average 

diameter 

eleventh 

year, inches 


Jonathan 

Jonathan 

Rome 

Rome 

Grimes 

Grimes 

Wagener 

Wagener 


Winter 

Summer 

Winter 

Summer 

Winter 

Summer 

Winter 

Summer 


16.1 
18.2 
15.4 
14.8 
12.7 
16.2 
11.9 
12.4 


17.24 
15.98 
15.88 
15.75 
16.00 
15.38 
14.65 
14.36 


19.51 
17.71 
14.35 
13.60 
15.30 
14.67 
12.25 
12.95 


7.43 
7.35 
6.58 
6.56 
6.71 
6.32 
5.82 
5.61 



tissue formation, active growth ensues. This apparently is the explana- 
tion of the results obtained with young peach trees in New Jersey 7 and 
with young apple trees in Oregon. 21 Soil conditions were such and the 
pruning was such, in time, kind and severity, that a vigorous new vegeta- 
tive growth was promoted following the pruning and terminal bud forma- 
tion was completed at a considerably later date. This condition may 
frequently result in an actual increase of food reserves at the time of leaf 
abscission, especially in sections with a late growing season, because of the 
greatly increased leaf surface. On the other hand if the pruning is of 
such character that carbohydrates and other elaborated foods are re- 
moved in considerable quantity and if it is done at a time when soil and 
tree conditions do not stimulate later growth the same season, there is 
not only an immediate reduction in size but reserves for the following 
season are depleted and growth the next year will be correspondingly 
restricted. Summer pruning under such conditions has a distinct 
dwarfing influence. 

In conclusion, then, it may be stated that summer pruning does not 
necessarily have either a dwarfing or an invigorating influence. It 
may have the one or the other, depending on the severity, kind and 
time of pruning (as related to the state of development of the plant, 
rather than to the exact date on which the priming may be done). 
Environmental conditions also, particularly nutrient supply, soil moisture 
and light, influence greatly the nature of the response from summer 
pruning. Consequently it should be employed as an orchard practice 
only when due consideration is given the several factors on which its 
results depend. The amateur or the careless grower cannot use it safely. 
The careful student of fruit growing can often employ it with reasonable 



444 FUNDAMENTALS OF FRUIT PRODUCTION 

certainty of the results and frequently will find it of great value. The 
results attending summer pruning in some of the best managed cane 
fruit plantations furnish ample evidence to this effect. 

Influence on Production. — The grower, however, is interested par- 
ticularly in knowing whether or not certain specific objects can be accom- 
plished — or accomplished more readily — by doing the work at one season 
rather than at another. This really is the question leading to most of 
the discussion over summer pruning. 

The opinion receiving general acceptance is expressed in the proverb, 
"prune in winter for wood and in summer for fruit." Quintinye 39 
states that summer pruning leads to the formation of fruit buds for the 
following crop. Hovey, 27 referring particularly to the apple and pear, 
states that it leads to the formation of fruit spurs and thus indirectly 
aids in fruit production. Quinn 38 recommends pinching back in summer 
to promote fruitfulness in the pear and Barry 2 recommends this practice 
even more generally for the same purpose. Waugh 51 states that summer 
pruning tends to promote fruit-bud formation. Cole, 13 Downing 17 and 
many others recommend summer pruning in preference to winter pruning, 
but because wounds made at that time heal more readily than those 
made at other seasons. On the other hand Pearson 37 states that summer 
pruning may either promote or repress fruitfulness, depending on how 
it is done. The general idea is that fruitfulness is promoted by summer 
pruning through checking growth or weakening the plant. 

Though the majority of the opinions just cited are from American writers, 
it should perhaps be stated that it is in European countries that the practice is 
most commonly employed and that it is in those countries that it is generally 
believed to be of particular value in promoting fruitfulness. In America there 
is a much greater diversity of opinion. Much of the apparent difference in 
results attending summer pruning in this country and in Europe is to be explained 
through the difference in the methods employed. The growers of this country 
mean by the term summer pruning a pruning similar in kind and in amount to 
that ordinarily done during the dormant season. On the other hand, summer 
pruning to the European fruit grower means something entirely different — for 
the most part a pinching or at least a pruning that can be done largely "with 
the thumb and forefinger." This type of pruning is employed in America neither 
in summer nor in winter. As explained later under Pinching the practice of 
summer pruning commonly employed in Europe is hardly applicable here be- 
cause of economic considerations and consequently the extensive European 
literature on summer pruning is only of incidental interest to most American 
fruit growers. 

In the section on Nutrition, data are presented showing that vigor 
of growth and productiveness are not necessarily antagonistic qualities. 
Indeed, the largest yields are always obtained from rather vigorous plants. 
The belief that increased fruitfulness should follow summer pruning as 



PRUNING— THE SEASON 



445 



generally practiced in America, is therefore based on two assumptions, 
both of which are fundamentally wrong. This is shown by some of 
the more recent investigations in this particular field — notably those 
in Virginia, 19 West Virginia 1 and Utah. 3 All these showed decreased 
production of flower clusters or decreased yields of fruit following the 
summer pruning of young trees just coming into bearing or with their 
bearing habits not yet well established and all report an accompanying 
decrease in vegetative growth. In one of the West Virginia experi- 
ments the yield of the summer pruned trees averaged barely a third of 
the yield from those receiving winter pruning. On the other hand 
Bedford and Pickering 4 in one series of experiments found flower-bud 
formation following summer pruning greater by 13 to 41 per cent, than 
following winter pruning, depending on the time of operation. Alderman 
and Auchter, 1 who found summer pruning a considerable check to fruit 
production in apple trees just coming into bearing, report no such general 
influence on mature trees. Table 16 summarizes the yields obtained in 
Idaho over a 7-year period from winter and from summer pruned plots. 
In every variety under trial summer pruning resulted in an increased 
yield. 

Table 16. — Average Yields in Pounds per Tree From Winter and Summer- 
pruned Trees 
(After Vincent™) 



Variety 



Pruning 



Yields 



1910, 
pounds 



1911, 
pounds 



1912, 
pounds 



1913, 
pounds 



1914, 1915, 
pounds pounds 



1916, 
pounds 



Total, 
pounds 



Jonathan. . . . 


Winter 


Jonathan. . . . 


Summer 


Rome 


Winter 


Rome 


Summer 


Grimes 


Winter 


Grimes 


Summer 


Wagener .... 


Winter 


Wagener .... 


Summer 



29.0 
33.9 
13.9 
13.9 
13.2 
20.0 
29.0 
54.3 



35.3 
21.3 
65.2 
30.0 
61.0 
71.0 
17.2 
59.4 



95.5 
95.5 
52.5 
58.5 
85. 1 
99.5 
67.0 
123.2 



127.8 

144.3 

58.8 

85.0 

101.6 

195.5 

22.0 

50.8 



257.4 

252. 1 
76.8 
80.0 

128.7 
88.5 
83.7 

159.0 



50.3 

51.7 

18.7 

23.0 

102. 1 

155.6 

6.2 

27.2 



239.4 
272. 1 
105.7 
160.4 
197.3 
108.3 
177.4 
215.5 



834.7 
870.9 
391.6 
450.8 
689.0 
738.4 
402.5 
689.4 



In commenting on these increases Vincent 49 says: "If the entire orchard had 
been summer-pruned there would have been an increase per acre during the 7 
years as follows: Jonathan, 30.02 boxes or an increase of 4.28 boxes per year; 
Rome, 49.7 boxes, or an increase of 7.1 boxes per year; Grimes, 50.6 boxes or an 
increase of 6.07 boxes, per year; Wagener, 240.9 boxes or an increase of 34.4 
boxes per year. Summer pruning therefore has increased crop production on all 
the plats and quite substantially on the Wagener." 

In neither the mature West Virginia trees nor the Idaho trees was 
summer pruning attended by an appreciably decreased vegetative 
growth. 



446 FUNDAMENTALS OF FRUIT PRODUCTION 

At first glance these records of yields from summer and winter pruned 
trees seem contradictory. As is the case with the corresponding records 
of shoot growth, however, they can be reconciled. It has been pointed 
out that fruit production depends on (1) the formation of fruit-producing 
wood and (2) on the proper functioning of that wood. Furthermore, 
different kinds of fruits have quite unlike fruiting habits and the processes 
culminating in fruit production may be quite different in one from those 
in another. The effect of summer pruning on fruitfulness, therefore, 
is not a simple question, but rather a series of questions each of which 
must be answered in turn. 

Among the major aspects of the summer pruning problem may be 
stated the following: (1) The concentrating effects of different kinds and 
amounts of pruning at various times during the growing season. (2) 
The relation of diverse summer pruning treatments to shoot growth 
both of the current and of the following season. (3) The influence on new 
spur formation. (4) The effect on fruit bud formation — on spurs and 
on shoots. (5) The relation to the intake of nutrients and to the manu- 
facture, translocation, storage and utilization of elaborated foods. (6) 
The influence on color and size of fruit. These questions are not entirely 
distinct; they are inter-related and inter-dependent. Since few data are 
available concerning some of them, any discussion at this time must of 
necessity be incomplete. It is attempted here on a few aspects only of 
the general problem, those which have more or less immediate practical 
bearing and on which the evidence seems reliable. 

Summer Pruning to Develop Framework. — Data have been presented 
concerning the influences of summer pruning on vegetative growth in 
general and on new shoot formation in particular. No further attention 
is devoted here to this problem except to indicate a rather special use 
of early summer pruning in developing the framework of young, strong, 
vigorously growing trees. 

Trees of many kinds growing under favorable conditions often develop 
shoots 23^2 or 3 feet — and sometimes more — in length during their second, 
third and fourth seasons in the orchard. Occasionally they make such 
growth their first season and shoots of this character are not at all 
uncommon as the trees grow older. Ordinarily most of this shoot growth 
is cut away in the annual dormant season pruning, some being taken out 
entirely and the terminal half or even three-fourths of each remaining 
shoot generally being removed. This heavy cutting back is necessary 
for securing a strong framework and a compact type of growth. The 
question naturally arises whether these trees can be pruned in mid- 
summer shortly after the shoots have attained a length equaling that to 
which they would be cut back at the usual winter pruning. This would 
then be followed by the production of secondary lateral shoots, many of 
which could be saved with little or no heading back at the following 



PRUNING— THE SEASON 447 

winter pruning. In this way two steps in the construction of the frame- 
work of the tree would be taken in one season and theoretically a year 
would be saved in growing the tree to producing size and in bringing it 
into bearing. This type of summer pruning, which includes both thin- 
ning and heading early in the summer (about July 1) was studied with 
apples in Oregon. 21 Though such varieties as Jonathan, Grimes, Yellow 
Newtown and Wagener summer pruned in this way did not make the 
equivalent of two seasons' ordinary growth in one summer, three success- 
ive years of such treatment resulted in trees comparable in size, fruit 
spur development and productiveness to winter pruned trees a year 
older. In other words a year had been gained in developing their frame- 
work and in bringing them into bearing. Observation led to the belief 
that this method of pruning is equally valuable in forcing the early de- 
velopment of both pears and sweet cherries. This special pruning prac- 
tice is desirable with young trees only under favorable growing conditions 
when they are making new shoots at least 2}^ feet in length and where 
the growing season is long enough to permit a proper maturity of the 
late secondary shoots. 

Summer Pruning as a Conservation Measure. — It has been stated 
before that the removal of any living portion of the top of a plant at any 
time deprives the plant of a certain amount of elaborated food material. 
This is true particularly of pruning in summer when the storage tissues 
have been depleted for the building of new structures. However, the 
removal of any portion of the top reduces somewhat the demand on the 
root system for nutrients and moisture; under certain conditions this 
reduction may enable the roots to supply the remaining parts with 
amounts nearer their requirements for growth. In this way pruning 
can be said to have a stimulating influence. In other words, it may be 
regarded as a conservation measure, making given amounts of moisture 
and nutrients go further; because these larger amounts of materials are 
available, certain parts may manufacture and store more elaborated 
foods than they could otherwise. This may be considered a concentra- 
tion effect. The concentration is limited to certain parts and in some 
instances other parts may suffer and perhaps the plant as a whole may be 
weakened. Apparently one of the more important objects that may be 
accomplished by pruning during the growing season is due to this in- 
fluence. 

This effect of summer pruning depends on many factors. Among the 
more important are: (1) the severity of the pruning, (2) its kind, (3) the 
exact stage of development of the plant at the time the pruning is done 
and (4) the soil conditions before, at the time of and after the operation. 

Independent of the other factors, it is evident that, within certain 
limits, the more severe the pruning the greater will be its effect in diverting 
into the remaining parts nutrients and moisture. However, a point is 



448 FUNDAMENTALS OF FRUIT PRODUCTION 

always reached, unless the operation is performed shortly before the begin- 
ning of the dormant season, when an increase in the severity of the pruning 
results in forcing into growth buds that otherwise would remain dormant 
until the following spring. At this point its general effect changes from 
conservation to dissipation since the new tissues demand not only soil 
nutrients and moisture but elaborated foods as well. The branches, 
canes or shoots remaining and perhaps the whole plant, are left weaker 
in that they are likely to enter the dormant season less richly supplied 
with elaborated food materials. In general the conservation effects of 
any pruning cease when it promotes greater utilization of reserve foods 
in the building of new tissue. Were these effects (that is, the ratio that 
they bear to the total effects) of summer pruning plotted in a curve as 
they vary with the severity of the pruning this curve would start close to 
the 100 per cent value with very light pruning and fall steadily with each 
increase in severity until the zero point is reached. Furthermore this 
general situation would obtain regardless of the kind of the pruning or of 
the exact time of the operation, though in no two cases could the curves 
be expected to be exactly parallel. 

Closely related to the stimulating effect of varying amounts of summer 
pruning is the influence of the stage of seasonal development at which it 
is done. In general a very early summer pruning, particularly if it 
consists in thinning out, is most effective in diverting the energies of 
the plant into other developing or already developed tissues. It may 
lead to greater elongation of shoots, to shorter internodes and more 
leaves, possibly to the formation of side branches or to several other 
growth responses or it may simply result in a more efficient functioning 
of the remaining tissues. This, for instance, is the general effect of the 
prompt removal of watersprouts, suckers or other shoots just as they are 
starting. If the pruning is done a little later, during the period of most 
rapid vegetative growth, it may have a concentrating effect (that is, 
lead to the greater accumulation of elaborated foods) or it may have the 
opposite effect and force out a crop of secondary shoots, the kind of the 
response varying with the severity and kind of the pruning. Pruning 
late in the growing season, if not too severe, is almost sure to have a 
concentrating effect (for the particular parts affected), since no new 
growth will take place to utilize the stored foods and there will be still 
further accumulations resulting from the increased supply of nutrients 
and of light. 

Of the two kinds of summer pruning, thinning out generally has a 
much greater concentrating effect than heading back. The latter 
practice, unless it consists in a mere pinching out of the terminals or 
unless it comes very late in the season, results immediately in the forma- 
tion of numerous secondary lateral branches. Their development 
consumes food materials that have been, or are being, manufactured and 



PRUNING— THE SEASON 449 

results in a shading of leaves lower in the tree and possibly in reduced 
rates of photosynthesis and of food manufacture. However, a light 
heading back or pinching of the terminals of the grape early in the season, 
thus temporarily checking new shoot growth, is said to aid materially 
the setting of fruit in certain varieties. 6 This is a concentration effect, 
though the practice is of special rather than general application. On the 
other hand thinning out has no such tendency to encourage the develop- 
ment of secondary; shoots certainly they are not formed to anything 
like the same extent as with summer heading. More light is admitted to 
the interior of the plant which is better supplied with nutrients and 
moisture and the result is an increased accumulation of elaborated foods. 
The results attending a well distributed thinning of the shoots and smaller 
branches would be more pronounced in this direction than those following 
a coarse or bulk thinning. 

When soil conditions, particularly moisture and nutrient supply, 
encourage new vegetative growth, summer pruning is much less likely to 
exert concentrating effects than it is when less moisture and less nitrogen 
are available. Indeed its influence may be the reverse, particularly if the 
summer pruning has been mainly heading back. Generally speaking, it is 
easier to secure the concentration effects of summer pruning when the 
available soil moisture and nitrates are not too high and when atmospheric 
conditions favor a high transpiration rate. These, it will be recognized, 
are the conditions under which it has been suggested by Chandler 10 that 
summer pruning can be employed advantageously as a moisture- 
conserving measure to prevent the wilting of partly grown fruits on 
heavily laden and vigorously growing trees. The influence of certain 
summer pruning practices on the formation of fruit buds, discussed a 
little later, is probably due to their concentrating effect. 

In a general way it may be stated that summer pruning is often 
very useful because of its influence in diverting the energies of the plant 
into other channels. In the average plant most of the watersprouts and 
suckers (except those used for renewal purposes) are worse than useless. 
They dissipate energies and yield little in return. Their prompt 
removal is a conservation measure and is particularly important in 
certain fruits like the grape and in nearly all young trees. The longer 
the delay in cutting them out the less is gained by removing them. 
Practically the same statement holds for the early summer removal of a 
portion of the barren shoots in the grape and certain other plants. 
Midsummer or late summer pruning may be desirable occasionally, in 
so far as it reduces transpiration losses and indirectly aids in the sizing 
and coloration of the fruit. 

It should be reiterated that the concentrating effect of pruning does 
not necessarily invigorate the plant as a whole. In fact it may have 
exactly the opposite influence, though certain parts are favored by the 

29 



450 FUNDAMENTALS OF FRUIT PRODUCTION 

process. Thus a heavily laden peach tree pruned in late July as a protec- 
tion against drought is probably weakened by the operation and may 
show the effects in the new growth put out the following spring, though 
the pruning operation enabled the fruit to mature properly. The 
situation is simply another aspect of a problem constantly encountered 
in pruning practice — that of subordinating or even eliminating one part 
in the interest of another. 

Influence on New Spur Formation. — The influence of summer pruning 
on new shoot formation and consequently on the fruit-producing wood 
in plants bearing on shoots or canes has been discussed. There 
remains consideration of its influence on new spur formation. Spurs are 
generally formed from lateral buds on the long growths of the current 
or of the preceding season. Only a certain percentage of these grow out 
into spurs, the number depending on many factors, among the more 
important of which are (1) the supply of nutrients and elaborated food 
materials available for their growth and (2) the relative stage of develop- 
ment or the size of the buds themselves. The influence of summer 
pruning on the supply of available foods has just been considered under 
the head of Concentration; consequently that aspect of the question 
need not be discussed further. 

Observation shows that in almost all species there are considerable 
differences in the size of the lateral buds on the long growths or shoots. 
Usually those on the basal portion are small and inclined to remain 
dormant unless stimulated into growth by some special pruning or 
other treatment; the buds on the median and terminal portions of the 
shoot are better developed and grow out readily, to form either shoots or 
spurs. Apparently their greater size and development is due largely to 
the better light supply and to the more favorable location for food manu- 
facture, of the leaves that subtended them. Obviously almost any 
pruning and particularly any summer pruning will influence the amount 
of light reaching the leaves on the remaining shoots. In many fruits sum- 
mer heading back, unless very light and done comparatively late in 
the season, encourages the formation of laterals or secondary shoots and 
consequently produces poorer conditions for photosynthesis in the lower 
parts of the plant. At the same time, as shown later under Pinching, 
it results in thickening the bark on the lower portion of the shoot and 
therefore in different food storage conditions that are associated with the 
change in the relative proportions of the several tissues. These effects 
may outweigh in importance those occasioned by greater shading. There 
is reason to believe that in at least some fruits summer heading acts as a 
stimulus to fruit-bud formation on the current season's shoots. On the 
other hand thinning out admits more light to the leaves on the lower 
part of the shoots and thus encourages the elaboration of foods and the 
formation of larger and stronger buds. Summer thinning therefore 






PRUNING— THE SEASON 451 

tends to encourage fruit-spur formation. This is in a sense another 
concentrating effect of summer pruning. It is evident from what has 
been said that the earlier in the season the pruning is done the greater is 
its influence in this direction. 

Gardner 21 has reported that in young apple trees not yet in bearing 
greatly increased fruit-spur formation follows early summer pruning 
in addition to winter pruning. This is not so much because of the better 
spur production from the buds left on the primary shoots after the 
summer pruning as because after the pruning many secondary shoots are 
produced on which the buds grow out readily to form new spurs the 
following season. In apples nearly all the buds on these late summer 
secondary shoots enter the winter in practically the same condition as, and 
are comparable in every way to, the buds on the median and terminal por- 
tions of the primary shoots. 32 In fact one of the most useful purposes 
served by the early summer pruning of young vigorously growing spur 
bearing trees like the apple is to increase the number of spurs over that 
secured by winter pruning alone. It is worthy of mention that spurs 
developing from these secondary late summer shoots are as a rule 
especially strong, vigorous and likely to produce fruit buds. 

Influence on Fruit-bud Formation. — In the section on Nutrition 
it is shown that, in all cases studied, fruit-bud differentiation is associated 
with carbohydrate accumulation in the immediate vicinity of the buds 
concerned. The work of Magness 33 on young apple trees indicates that 
this accumulation takes place principally where there is the greatest 
effective leaf area. In other words, within certain limits those spurs 
that have the largest and best lighted leaves accumulate the largest 
reserves of carbohydrates and differentiate the most fruit buds. He 
found that by partial or complete defoliation of spurs well supplied with 
leaves, fruit-bud formation on these spurs could be entirely prevented, 
even though adjacent spurs retaining their full complements of leaves 
formed fruit buds freely. Similarly he found that the formation of 
lateral fruit buds took place only in the axils of good sized, well lighted 
leaves. 

Magness 33 summarizes his results as follows: "Fruit-bud initiation will not 
take place, and fruit buds will not form in most varieties in the absence of a fair 
amount of leaf area in the tree. 

"Food material stored in the tree through the dormant season is apparently 
stored largely in the tissue adjacent to the leaves in which it was manufactured. 
This is shown by the fact that the defoliated portion does not develop as strongly 
and well during the spring following the treatment, as does the undefoliated 
portion. 

"Leaf area in one part of the tree will usually not supply food material to 
the buds in another part to the extent necessary to cause them to become fruit 
buds. Defoliating one-half of a tree has little influence upon the undefoliated 



452 FUNDAMENTALS OF FRUIT PRODUCTION 

portion, but that part which is defoliated functions as it would if all the leaves 
had been removed from the whole tree. 

"Removing the same number of leaves, without any pruning, has practically 
the same effect upon the fruit-bud formation for the immediate year following 
that a summer pruning, removing leaves from the same position, would have. 

"Buds on 1-year wood, in areas from which the leaves have been removed 
are slower in starting out into growth, and make a weaker growth the following 
spring than do other buds on the same shoots not defoliated. This is more 
noticeable in some varieties than in others. 

"One shoot seems to be very largely independent of other shoots about it so 
far as fruit-bud formation is concerned. It is apparently largely dependent upon 
its own leaves for nourishment. 

"Removing leaves from individual spurs tends to prevent the formation of 
fruit buds upon those spurs, although it does not entirely check the development 
of flower parts. 

"On those spurs which form fruit buds, notwithstanding defoliation, the 
blossoms are, on the average, considerably later in opening in the spring. 

"Axillary buds of the Wagener seem to be almost entirely dependent upon 
the immediate subtending leaf for the carbohydrate supply with which they are 
nourished. Removing the subtending leaf entirely prevents fruit-bud formation. 
Buds so treated either remained entirely dormant during the following growing 
season or pushed out into very weak growth. Very few of them showed a 
development approaching normal." 

Magness' work may explain incidentally why the basal portions of 
shoots often produce relatively fewer fruit buds than the median and 
terminal portions. The basal portions are poorly lighted and, assuming 
leaves of equal size, they would manufacture smaller amounts of elabo- 
rated foods. Neither spurs nor shoots can be expected to differentiate 
fruit buds freely if they are heavily shaded. Summer pruning, however, 
may admit more light both to the spurs and to the basal portions of 
the shoots at the same time it concentrates the supply of nutrients. 
This direct influence on the factors associated with fruit-bud formation 
could hardly help but influence more or less directly the relative number 
of fruit buds. Obviously early summer pruning comprising thinning 
out instead of heading back would have the greatest influence of this 
kind. No pruning practice after fruit-bud formation for the season 
is completed could conceivably have any influence in this direction and 
heading back with the formation of many secondary lateral branches 
would cause still heavier shading and reduce rather than increase fruit- 
bud formation. Doubtless many of the cases in which summer pruning 
has failed to produce an increased number of fruit buds have been due 
to its consisting mainly in heading back or being done too late to 
have any important influence in this direction. Experience shows that 
a light or moderate early summer thinning of the shoots of those trees 
such as the peach that bear laterally on shoots aids greatly in the forma- 



PRUNING—THE SEASON 453 

tion of fruit buds on the basal and median portions of those shoots. 
Though such summer pruning may not result in any considerable increase 
in the total number of fruit buds, it does favor fruit-bud formation 
in more desirable places and is well worth while. 

Influence on Fruit Color. — In the apple, peach and certain other 
fruits the development of the red colors in the skin of the fruit depends 
mainly on sunlight. With those fruits summer pruning naturally 
influences their coloration, particularly if the pruning consists mainly 
in thinning out. Vincent 49 reports that summer, as compared with 
winter, pruning the apple in Idaho resulted in an increase of 33 per cent, 
of extra fancy apples in Jonathan, 32 per cent in Rome and 5 per cent 
in Wagener, the grading being mainly on the basis of standard commercial 
color requirements. The coloring of certain other fruits, as plums and 
grapes, does not depend on light reaching the fruit itself, though pig- 
ment formation depends on carbohydrate manufacture in near by 
leaves. Consequently summer pruning is of less direct aid in the colora- 
tion of these fruits. Bioletti, 6 however, states that judicious summer 
pruning may occasionally favor the coloring of the fruit in certain grape 
varieties. Presumably this influence is exercised through the better 
lighting of the foliage near the fruit clusters. 

Most fruits develop their color late in the growing season or shortly 
before ripening. Consequently summer pruning to promote a better 
coloring of the fruit may be done comparatively late. In pruning for 
this purpose caution should be exercised; too severe or too early summer 
pruning is likely to result in more or less sunburn of the fruit. 

Summer Pinching. — It is impossible to distinguish clearly between 
what is termed pinching and what is usually termed topping or heading 
back. The difference between the operations is simply in the maturity of 
the tissues at the time the operation is performed and in the relative 
amount of new growth removed. In some species, as for example the 
rambles, pinching leads to considerable branching of the pinched shoots; 
in many others it may be attended by very little branching, one or two of 
the subterminal buds promptly growing out to replace the leader. Conse- 
quently its general effect may be concentration or dissipation and dilution, 
depending on the species and on conditions. Summer pinching has been 
much used in European fruit growing and in the growing of fruits under 
glass. In this country it has been used mainly with the brambles and with 
grapes, though occasionally it is helpful in checking or directing growth 
in some of the other fruits. 

There seems to be much difference of opinion among growers and 
investigators as to the wisdom of summer pinching of brambles. Both 
satisfactory and unsatisfactory results have been reported. Apparently 
much depends on the time of the operation ; furthermore varieties respond 
quite differently to the same treatment. Macoun 31 has reported that at 



454 FUNDAMENTALS OF FRUIT PRODUCTION 

Ottawa, Canada, red raspberries pinched back in early summer and thus 
forced to branch, generally yield less than untreated plants. Since 
Kenyon, Loudon, King, Hansell and Miller (red raspberries) do not branch 
freely, they should never be summer pinched. 45 The main advantage 
claimed for summer pinching is that it results in a lower, more compact, 
bushy plant with mechanically stronger canes than those that are un- 
headed and unbranched. Consequently they hold up their fruit better 
and require less trellising. Dewberries which usually require trellising 
are seldom summer pinched. It is generally agreed that if raspberries or 
blackberries are to be summer pinched the operation should be performed 
early, when the shoots are only 18 to 24 inches high or perhaps even 
before this. 9 Pinching higher or cutting back to this point at a later date 
is likely to result in weak, late-maturing laterals that are especially sub- 
ject to winter injury and are less likely to give rise the following year to 
good fruiting shoots. Blackberries and black raspberries generally 
respond better than red raspberries to summer pinching. Pinching the 
ends of the growing shoots just before blossoming has been stated 
to aid sometimes in the setting of fruit in the grape; it is thus a partial 
remedy for "coulure." 6 Bioletti 6 mentions pinching as sometimes useful 
also in protecting grapes from sunburn by causing the shoots, through 
more rapid lignification, to remain more upright and to furnish more shade 
for the fruit clusters. But little evidence is available concerning the 
influence of summer pinching on fruit-bud formation in the grape and at 
present it cannot be recommended confidently for any effect of this sort. 
The early and repeated pinching back of shoots of the apple and pear 
to stimulate the development of fruit spurs and fruit buds has been dis- 
cussed freely. Thomas 46 states that "by pinching off the soft ends of the 
side-shoots after they have made a few inches of growth — the sap imme- 
diately accumulates, and the young buds upon the remainder of these 
shoots, which otherwise would produce leaves, are gradually changed into 
fruit buds. To prevent the breaking of these buds into new shoots by too 
great an accumulation of the sap, partial outlet is left for its escape 
through the leading shoot of the branch, which at the same time is effect- 
ing the desired enlargement of the tree. ... It often happens, and espe- 
cially when the pinching is done too early, that the new buds send out 
shoots a second time the same season. When this occurs, these second 
shoots are to be pinched in the same manner as the first, but shorter; and 
third ones, should they start, are to besimilarly treated." Barry, 2 Rivers 41 
and others recommend the same treatment for the same purpose and these 
early authorities have been followed by many later writers. Recently 
Ballard and Volck 50 in California have shown that, by two or three repeated 
summer pinchings, fruit spurs bearing fruit buds can be developed from 
watersprouts of the apple in one season. They found also that normal 
shoots throughout the tree respond in the same way to similar treatment. 



PRUNING— THE SEASON 



455 



Gaucher 23 recommends early summer pinching in spurs which are growing 
out into vegetative shoots. He states this pinching usually stops further 
growth from the terminal bud and forces out at lower points on the spur 
lateral buds that otherwise would remain latent. These then develop 
into branch spurs that often form fruit buds the first season. If a single 
pinching does not result in fruit-spur and fruit-bud formation, a second 
pinching is recommended. 

Goumy 25 studied the influence of summer pinching on the subsequent 
development of bark and wood; some of his results are summarized in 
Table 17. Pinching obviously has led to a proportionally greater 
development of the bark. Goumy found also some difference between the 
relative amounts of bark and of wood in the spurs on the year old growth 
of pinched and unpinched spurs. The determination of just what these 
differences in relative amounts of bark and wood signify in terms of nutri- 

Table 17. — Influence of Summer Pinching on Relative Thickness of Bark 
and Wood in the Pinched Shoot of the Pear 

(After Goumy 2i ) 



Tissue 


Shoot not pinched 


Shoot pinched 


Pith 


2.3 
5.5 
2.25 

1.0 
2.2 
0.6 
1.6 
0.6 


2.8 


Wood 


3.7 


Bark 


3.4 


Bark tissues in particular: 

Epidermis 


1.0 


Cortical parenchyma 


4.4 


Sclerenchyma 


0.5 


Cortex 


3.0 


Cambium 


0.6 



tive conditions and food reserves is difficult, but presumably they favor 
fruit-bud formation in the pinched shoots. 

However, summer pinching has been practiced frequently for the 
purpose of promoting fruit spur and fruit-bud formation and has not 
secured the expected response. In general it may be stated that, though 
the practice may produce satisfactory results if followed properly by succes- 
sive pinching of secondary and tertiary shoots, the amount and kind of 
labor involved are such as to make it of doubtful value in the commercial 
fruit plantation in America. When trees are grown as standards other 
measures or practices that are available will call forth more of a mass 
response and will provide at much less expense the requisite number of 
fruit spurs and fruit buds. 

The early summer pinching of shoots in young trees for the purpose 
of subordinating those that are not wanted for permanent framework is 
only occasionally employed but is frequently to be recommended. In 



456 FUNDAMENTALS OF FRUIT PRODUCTION 

newly planted trees the buds within a short distance from the ground 
often start to grow. Generally the resulting shoots are promptly rubbed 
off or they are pruned away after they have been allowed to grow a year. 
In either case the growth of the upper branches is very likely to be checked. 
If these lower shoots are promptly pinched back so as to leave three or 
four leaves apiece the upper shoots are not checked in their development, 
the trunk is shaded and the food materials that their leaves manufacture 
will be of considerable value in promoting a vigorous growth the following 
season, after which they can be removed. Similarly in trees that have 
been growing in the orchard for 1, 2 or 3 years, are formed many shoots 
that ordinarily are removed at the following dormant-season pruning. 
Their growth reduces somewhat the development of those desired for the 
permanent framework. Pinching them back early in the season sup- 
presses them and the nutrients and moisture are largely diverted into other- 
parts, but at the same time their leaf surface serves to manufacture 
elaborated foods for the current and the following seasons. 

Summary. — On the whole but little difference is likely to result from 
pruning at different times during the dormant season, though in certain 
fruits early pruning is followed by earlier foliation in the spring. This is 
a factor of commercial importance in grape culture. Very late pruning 
generally leads to more bleeding than earlier pruning. Bleeding from 
pruning wounds seldom harms the plant. 

Summer pruning may have a dwarfing or an invigorating influence 
(as compared with a corresponding winter pruning), depending on its 
severity, kind, the stage of development of the plant and on environ- 
mental conditions — particularly nutrient supply, soil moisture and light. 
A light summer thinning encourages fruit-spur formation through favor- 
ing the development of larger and stronger lateral buds from which spurs 
are formed. The same practice promotes fruit-bud formation also if the 
work is done early enough in the season. Heading back tends to stimu- 
late purely vegetative growth. Judicious summer pruning is more or 
less a conservation measure. This applies particularly to the removal 
of watersprouts and other superfluous growth. In very strong vigorously 
growing trees 2 to 5 years old early summer pruning results in encouraging 
a late secondary growth and this may be a means of hastening the general 
development of the tree if there is a long growing season and other condi- 
tions are favorable. A light summer pruning may aid materially the 
coloration of fruit in certain species. 

Summer pinching in general encourages the development of sec- 
ondary shoots. This is often desirable in the culture of the bramble 
fruits. Pinching may be used also to subordinate individual shoots and, 
in the spur-bearing species, it may result in their developing into spurs. 
This practice is of doubtful utility, however, in the culture of standard 
trees. 



CHAPTER XXV 

PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 

In a preceding chapter were discussed some of the more important 
general or mass effects of pruning. Mention was made also of the more 
specific influence of certain practices on fruit-spur, shoot or fruit-bud 
formation in particular parts of the tree, though this concerned the 
general aspects of those questions rather than the particular applications 
presented by different fruit plants. Another chapter attempts to explain 
in some detail the fruit bearing habits of the more common fruits. There 
remains for discussion the adaptation of pruning practices to plants hav- 
ing these different methods of bearing so that maximum annual produc- 
tion may be obtained along with the form of tree or plant most conducive 
to long life and economy in production. It should not be inferred, 
however, that all fruit plants with the same fruiting habit should be 
pruned alike. Their general growing habits, that is, the amount and 
character of their new vegetative growth, may be quite different and 
necessitate equally diverse pruning treatments. Though the Winter 
Nelis pear has essentially the same bearing habit as the Maiden Blush 
apple, the two must be pruned quite differently because they are so 
unlike in their vegetative growth and the red raspberry with essentially 
the same fruiting habit as the black raspberry should be pruned more 
severely because of its great tendency to sucker; many other instances 
might be cited. 

Broadly speaking, pruning may be said to influence fruit-bud and 
fruit formation — bearing habit — in two ways, directly and indirectly. 
Its most important direct influence is to thin the crop through the removal 
of actual or potential fruit-bearing wood. Another rather direct influence 
is its effect on the location or distribution of fruiting wood, both spurs 
and shoots. Its indirect influence is effected mainly through changing 
nutritive conditions within the tree and consequently limiting or encour- 
aging fruit-spur or fruit-bud formation. As these indirect effects have 
been considered rather fully in the preceding chapters but little attention 
is given them here. Furthermore no attempt is made to discuss the 
influence of different pruning treatments on the fruiting habits of any of 
the tropical or subtropical fruits or of a number of the less common and 
less important deciduous fruits. 

Pruning the Apple and the Pear. — As has been pointed out, apple and 
pear flowers are for the most part borne terminally on short growths 

457 



458 FUNDAMENTALS OF FRUIT PRODUCTION 

springing from terminal buds on other short growths, or spurs. Indi- 
vidual spurs are wont to bear only every other year, though annual 
bearing spurs are not rare and are common in trees of certain varieties. 
More frequently, however, individual spurs fail to produce even every 
other year, bearing perhaps only once in 3 or 4 years, or very irregularly. 
These spurs may live many years and there is nothing in their manner of 
growth to necessitate a deterioration in efficiency as they grow older. In 
reality, however, they flower and, more particularly, set and mature 
fruit, much less regularly as they increase in age. 52 Without doubt this is 
due to unfavorable nutritive conditions induced by crowding and compe- 
tition with other parts of the tree for food, moisture and light. Records 
show, nevertheless, that even very old spurs may bear good fruits and that 
when strong and vigorous they are more efficient fruit producers than 
those that are much younger but lacking in vigor. 52 Roberts 44 has 
reported a marked correlation between the vigor of spurs, as measured 
by the length of each year's growth and by the number and area of their 
leaves and performance in flower-bud formation. Spurs of medium 
length with relatively large leaf areas and consequently with the means 
of accumulating reserves of elaborated foods are more likely to form 
fruit-buds. 

Heavy annual production, then, would seem among other things 
to depend on (1) the formation of an adequate supply of fruit spurs, 
(2) the retention of those already formed and (3) maintaining all of 
them in a vigorous condition so that they may flower and fruit regularly. 
These requirements plainly cannot be met or supplied by any single 
pruning practice or by any combination of pruning practices. They 
depend on many factors, chief among which are nutritive conditions 
within the plant, which, in turn, are influenced most readily by ferti- 
lizers and various systems of soil management. Pruning, however, 
is important in this connection. 

The Formation of Fruit Spurs. — As pointed out elsewhere, maximum 
fruit-spur formation is encouraged by leaving the trees unpruned or by 
pruning them very lightly. Such treatment or lack of treatment leaves 
the largest possible number of buds from which spurs may develop; 
consequently an approach to this treatment is recommended to induce 
bearing in a short time. Formerly the artificial bending of long shoots 
was quite generally recommended to make them more fruitful through 
the formation of fruit spurs. However, recent investigation indicates 
that this practice is of doubtful value and certainly is not to be recom- 
mended under average field conditions. 22 Experimental work at the 
Oregon Station has shown that when certain shoots are selected for 
removal in young apple trees, new fruit-spur formation is favored by 
leaving those that are vigorous and comparatively upright. 20 As the 
trees become older and possess fruit spurs in numbers sufficient to pro- 






PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 459 

vide full crops less attention need be given to obtaining new spurs. Some 
of the old spurs die out or are lost through accident and new spurs are 
needed tore place them and of course the numbers increase as the tree 
grows older. Usually, however, more spurs form than the tree can 
support to advantage and it is only in the tree between 4 and 6 or 8 years 
of age that there is need of definite effort to encourage their development. 

Very rarely do new spurs form directly on the old wood from either 
latent or adventitious buds. In case the spurs in the lower-interior part 
of the tree die out or are destroyed the only way to develop new spurs in 
that region is to prune back the top of the tree somewhat heavily. This 
will force out watersprouts from latent or adventitious buds. At the 
same time there should be enough thinning out to permit free access 
of sunlight and thus promote the development of large leaves and large 
lateral buds which a year later may develop into fruit spurs. These 
watersprouts are then treated in very much the same way as the tops of 
trees just coming into bearing; the same may be recommended for the 
strong vigorous growth in trees recently "dehorned" or recently 
topworked. 

Retaining Spurs Already Established. — Since the spurs of the apple 
and pear bear fruit repeatedly they should obviously be retained as 
long as they remain efficient producers. Yet many growers remove 
them unnecessarily at the time of pruning or permit their useless destruc- 
tion by careless pickers. In some varieties particularly, as for example 
the Esopus (Spitzenburg) apple, new spurs do not readily develop to 
replace the old, because of the difficulty in obtaining sucker growth in 
the interior of the tree; hence the loss of any considerable number of 
spurs is likely to render those portions of the tree permanently barren. 
There is often occasion for pruning out some of the fruiting wood of the 
apple and pear; however, this should be done with caution and with a 
clear understanding of the problems involved in replacing it. The 
advisability of much thinning of the crop by means of pruning is ques- 
tionable in these fruits. The ultimate result of the loss of spurs from 
the interior and lower portions of the tree is the forcing out and up of 
its bearing surface. Eventually the active fruiting wood will be around 
the outside and in the top of the tree with the major portion of the interior 
unproductive. When a crop is so distributed, its weight places the 
greatest possible strain upon the crotches and the tree is subject to 
greatest injury from storms and winds. Much of the breakage in the 
older orchards is associated with this condition, which can be largely 
avoided by thinning out which limits the formation of new fruit spurs and 
at the same time keeps the older spurs productive. 

Keeping Spurs Strong and Vigorous. — The superiority of vigorous 
fruit spurs over those that are weak has been mentioned repeatedly. 
They flower and set fruit more frequently and are much more likely to 



460 FUNDAMENTALS OF FRUIT PRODUCTION 

bring their fruits to maturity. Indeed, some question may be raised 
as to whether the very weak spurs, those that annually push out only 
two or three small leaves and rarely or never form fruit buds, are of any 
real benefit to the tree. They draw on the supply of moisture and 
nutrients obtained from the soil and they can yield but little elaborated 
food in return. Furthermore, observation indicates that forcing such 
spurs into vigorous growth, once they become weakened, is extremely 
difficult. Heavy pruning, alone or combined with certain cultural 
treatments, may force them to grow out into new shoots and later these 
shoots may give rise to fruit spurs; however, to reinvigorate them and 
make them form fruit buds without an intervening shoot growth is 
very difficult after they have ceased to function satisfactorily for several 
years. Therefore keeping fruit spurs in a vigorous condition from the 
start is doubly desirable. 

The vigor and growth of individual spurs depends on (1) the supply 
of moisture and nutrients from the roots and (2) the supply of elaborated 
foods stored more or less locally. This locally stored supply in turn 
depends largely on manufacture at or very near the point in question. 
Both of these factors are influenced by many cultural practices. Pruning 
may be a means of modifying, at least temporarily, the supply of moisture 
and nutrients available for the spurs that are left, through diverting 
to them large amounts before intake is correspondingly reduced. This 
effect of pruning can be obtained more readily by fertilizing, tillage, 
irrigation, mulching or other soil treatments. It may be pointed out, 
however, that though the effects attending these other cultural opera- 
tions and those attending pruning are quite similar, in the one instance 
there is a general influence on the vegetative activities of the tree while 
pruning has a more specific influence on certain of its parts or local 
regions. 

Pruning is a more important means of influencing the accumulation 
of elaborated foods, through admitting more or less light to the spurs. 
As has been pointed out, the general effect of heading back is to thicken 
the top, cause more shading and thus probably decreased carbohydrate 
manufacture in the lower and interior parts of the tree. On the other 
hand thinning out tends to have the opposite effect. Since the removal 
of spurs by thinning (either the removal of individual spurs or small 
spur-bearing branches) has as great a concentrating effect on nutrients 
as an equivalent heading back, it is to be regarded as the most important 
pruning practice in this respect. Indeed it is about the only pruning 
practice that always tends to increase longevity and regularity of bearing 
in fruit spurs. Consequently the heading back that is done in bearing 
apple and pear trees should be limited to that required to keep the tree 
from becoming too tall and too spreading for the mechanical support 
of its crop and for convenience in various orchard operations. In 



PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 461 

other words heading back should be done principally for the purpose 
of training, thinning out serving principally to affect its bearing habits. 

Summary of Usual Pruning Treatment. — Briefly, the general pruning 
treatment recommended for the apple and the pear, considering their 
growing and bearing habits and their responses to different types of prun- 
ing, may be stated as follows: During the first few years in the orchard, 
assuming at least a moderately strong growth, the tree should be pruned 
rather severely (beginning with perhaps a 75 per cent pruning) and this 
should consist in both thinning out and heading back, with the emphasis 
perhaps on heading back. This heavy pruning is for the purpose of 
properly developing the framework of the tree. If it has made a weak 
growth, pruning should be correspondingly lighter. As the tree becomes 
older, pruning gradually decreases in severity until at 6 or 7 years, when it 
reaches bearing age and size, very little is done. As pruning slowly 
lessens in severity it gradually changes in kind, consisting less in heading 
back and more and more in thinning out. This general procedure devel- 
ops a fruit-spur system and brings it into bearing. After the tree is once 
in bearing, pruning slowly increases in amount but continues to be 
mainly a thinning out; this thinning should comprise the removal of small 
limbs throughout the top rather than the cutting of a few large limbs. 
When this plan is followed there is some thinning of fruit spurs and of the 
fruit crop, overbearing is prevented and the length of life, regularity of 
bearing and efficiency of individual spurs are promoted. 

Spedial Suggestions for Unusual Fruiting Habits. — Certain varieties 
of the apple and the pear have been said to bear many fruit buds termi- 
nally or laterally on long shoots. This is particularly common during 
the period when they are just coming into bearing. Under these cir- 
cumstances greater care must be exercised against the unnecessary removal 
of any new shoots and heading back should be reduced to a minimum 
until the trees have a better developed fruit spur-system and are bearing 
a considerable percentage of their crop on it. The production of lateral 
fruit buds on long shoots, it should be noted, presents a case quite similar 
to that of the peach and consequently the pruning of such trees should 
resemble that ordinarily given peach trees as much as it does that of the 
average apple or pear variety. However, most of these lateral fruit buds 
in the apple are borne on the terminal half or even third of the shoot, 
while a considerable percentage of those of the peach are found on the 
basal half. This necessitates much more care in heading back the fruit 
bearing shoots in these particular varieties than is requisite in the peach. 

Pruning the Peach. — The peach is perhaps the best known repre- 
sentative of that group of fruits which "bear lateral fruit buds on long- 
growths or shoots. These buds contain flowers only and with their 
falling, or with the maturing of the fruits which develop from them, that 
portion of the branch to which they were attached becomes barren. 



462 FUNDAMENTALS OF FRUIT PRODUCTION 

Neither fruits nor flowers are again borne upon it. New growth develops 
from the terminal bud or from lateral leaf buds at some of the non-flower- 
ing nodes or in some instances from adventitious or latent buds lower in 
the tree. It is therefore characteristic of the peach to have its fruiting 
wood carried a foot or two further out and up each year, leaving long 
stretches of non-fruiting wood that serves only as a connecting link 
between the fruiting periphery of the tree and its root system. 

Seldom does the peach tree of bearing age fail to differentiate enough 
fruit buds for a heavy crop. In fact it commonly produces many more 
than are desired, so that some pruning is advisable for the purpose of 
thinning the crop. Furthermore, since the fruit buds are produced each 
year on the new wood of the current season there is no danger of rendering 
the tree unproductive for a period of several years, as in the apple or the 
pear, by cutting away its fruiting wood. Therefore the two main prob- 
lems in pruning this fruit are to thin the crop and to "keep the tree within 
bounds," that is, to prevent its fruiting wood from developing so far away 
from the trunk that propping, picking, spraying and fruit thinning involve 
too much expense. Almost any kind of pruning serves the latter purpose 
if it is severe enough; on the other hand the location of the new fruiting 
wood and the distribution of its fruit buds depend very considerably on 
the type of pruning that is employed. In fact it would not be far from 
correct to say that in the bearing peach tree the severity of pruning 
should be governed largely by the amount of crop thinning required and 
its kind should be determined by the desired distribution of the following 
season's fruiting branches and fruit buds. 

When and How Severely. — The bearing peach tree should be pruned 
lightly or heavily, depending on whether it gives promise of bearing just 
enough or too much, if little or no pruning is done. As a rule prospects 
cannot be estimated accurately until the trees are in bloom or even until 
the fruit has set, on account of danger from late spring frosts. Conse- 
quently it is wise to wait until that time and then to prune with the aim 
of providing as nearly as possible a full crop but still of reducing the labor 
of fruit thinning to a minimum. If crop prospects are ruined by a late 
frost the trees can be dehorned advantageously, because this heavy 
pruning will not result in any loss of fruit and since new growth for the 
following season's production will be forced to develop from the main 
scaffold limbs, the bearing surface will be lowered and made more com- 
pact. If midwinter or late winter freezing destroys the fruit buds this 
same type of pruning can be done earlier. 

Pruning to Secure Most Favorable Location of Fruiting Surface. — 
The usual method of pruning the bearing peach tree comprises such thin- 
ning out as seems necessary, this thinning consisting generally in the 
removal of wood from the center of the tree so as to provide an extreme 
open center. In fact the average peach tree as found in the commercial 









PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 463 

orchard illustrates more nearly the vase or goblet shaped form than almost 
any other species. This thinning out is then followed by as severe head- 
ing back of the shoots as is compatible with leaving enough good fruit 
buds — or flowers if the operation has been delayed until the blooming 
season — to provide for a full crop. If the number and distribution of 
buds is such that the heading back can be rather severe the new shoot 
growth will be forced to come out rather low and the tree will be kept 
relatively compact, though the fruiting wood of the following season will 
be necessarily somewhat farther out from the trunk than that of the 
current season. 

One result of the heading back will be a crowding of the new shoot 
growth; this will increase with the severity of the heading back. The 
result is comparatively long slender shoots, from whose nodes the leaves 
soon fall because they are shaded. Only leaf buds will be formed in 
their axils; these will be small and quite likely to remain latent the 
following year. Fruit buds are formed chiefly on the median or apical 
portions of these crowding shoots or on their secondary lateral branches. 
This necessitates a less severe heading back the following spring if fruit 
buds sufficient in number for a good crop are to be left and the bearing 
portion of the tree is pushed farther away from the trunk. Some shoots 
will probably develop in the interior of the tree from latent or adven- 
titious buds on the main limbs. These should be saved for renewal 
purposes, though usually it is only a matter of time before a general 
"dehorning" becomes necessary in order to lower the top and make 
the tree sufficiently compact for economical production. 

A practice seldom employed, but frequently desirable, is an early 
summer thinning out of the new shoots. Ordinarily this should be done 
in late June or early July, considerably before terminal bud formation 
is under way. It reduces crowding and the remaining shoots are less 
likely to become long because their internodes remain shorter. Their 
leaves are better lighted and those at the basal nodes persist through the 
season instead of falling prematurely. Consequently fruit buds form at 
these basal nodes as well as at the median or distal. This makes it 
possible to head back much more severely the following spring and still 
leave provision for a full crop. The fruiting zone is not carried so 
far from the trunk each year and dehorning is not so frequently necessary. 
Furthermore, the fruit buds at the more basal nodes enter the dormant 
period at a relatively less advanced stage of development than those 
farther out on the shoots. This makes them somewhat more resistant 
to winter cold and a little slower in opening the following spring. The 
practice also results in the development of many very short shoots that 
amount almost to fruit spurs bearing lateral fruit buds — a fruiting habit 
closely resembling that of the apricot or almond. This means in effect 
a tree that mechanically is much stronger than the average. The summer 



464 FUNDAMENTALS OF FRUIT PRODUCTION 

priming here suggested could easily be overdone. It should not remove 
so much new growth that the developing fruit is subjected to danger 
from sunscald or that the formation of secondary shoots is stimulated. 
It should be well distributed through the top and outer portions of the 
tree, as its effectiveness depends on making possible a better distribution 
of sunlight to the leaves on the lower portions of the new shoots. If 
carefully done it reduces greatly the amount of shoot thinning that will 
be required the following spring and the yearly pruning treatment really 
becomes a summer thinning out and a winter heading back. Inci- 
dentally it is of considerable aid in promoting coloration of the fruit. 

Pruning the Sweet Cherry. — Typical of that group of fruits whose 
flower buds are borne laterally on short spurs and give rise to an inflores- 
cence only is the sweet cherry. The terminal of the sweet cherry spur is 
always a leaf bud by which the growth of the spur is continued each year. 
New spurs originate from some of the lateral leaf buds on the shoots of the 
preceding season and new shoot growth proceeds from other lateral buds, 
from terminal buds on shoots, from latent or adventitious buds on the 
older wood and occasionally from the terminal buds of spurs. However, 
comparatively few shoots arise from buds of the last two classes in the 
sweet cherry. The lateral buds on the year-old shoots of young vigor- 
ously growing trees are little inclined to produce spurs, but either grow 
out into new shoots or remain dormant. Consequently the young trees 
of this species are thick brushy growers, strongly vegetative in character 
and often slow in coming into bearing. Old trees of the same species 
present a rather sharp contrast to this condition. Most of the lateral 
buds on their shoots produce spurs or remain dormant. Often new shoot 
growth is produced mainly from the terminal buds of the last year's 
shoots, the result being a tree that is markedly reproductive and often 
lacking in vigor. 

As the problem in the young tree is first to secure a strong framework 
and then a good equipment of fruit spurs, much as in the apple and 
pear and as its shoots and spurs originate from buds in the same locations, 
its pruning treatment the first few years should correspond closely to 
that of those fruits. In other words pruning should be fairly heavy at 
first, gradually decreasing in amount till at 6 or 7 years little is 
done. At the same time it should change gradually from a treatment 
which consists largely in heading back to one which consists almost 
entirely in thinning out. 

As the tree becomes older, however, its pruning treatment should div- 
erge gradually from that customarily given the apple or pear. Its natural 
tendency to produce large numbers of fruit spurs obviates the necessity 
of employing any treatment to encourage greater spur and fruit bud 
production. At the same time this growing habit results in a fairly 
open top in which the foliage is well exposed to light. On the other 



PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 465 

hand measures should be taken to promote a greater vegetative growth, 
particularly in those varieties or under those conditions that tend toward 
the development of new shoots from terminal buds only. Otherwise 
long pole-like fruiting branches, subject to much injury from the wind 
when heavily loaded with fruit, will develop. Heading back to promote 
branching, however, must be done with considerable care. If the 
heading is into 2-year, 3-year, or older wood new side branches are not 
likely to form and the limbs in question are subordinated to an unim- 
portant position in the tree. Heading back to near the base of the one- 
year old shoots is much more likely to induce the branching desired, 
though this alone is often rather ineffective in large trees somewhat 
lacking in vigor. A certain amount of pruning back to 2-year, 3-year 
or older laterals is often effective in keeping the tree within bounds. 
There is little occasion to do much thinning out in the sweet cherry tree 
that is well in bearing and the heading back is mainly for the purpose of 
lowering the top and correcting form. Dehorning is seldom resorted to 
because of the poor response in new shoot growth that often follows this 
operation and because of the time required for the formation of a good 
supply of new spurs before the tree can again come into heavy bearing. 

Generally speaking, then, the pruning of the bearing sweet cherry 
should be light in amount and for correcting and improving shape. On 
account of the growing habit this means that it will consist largely in 
heading back. Other orchard practices, such as cultivation, irrigation 
and fertilization, should be counted on to encourage a strong new shoot 
growth which can be headed back to promote branching and compactness 
of tree. 

Pruning the Almond, Apricot, Plum, and Sour Cherry. — As has been 
stated in the classification of fruiting habits, the almond, apricot, plum 
and sour cherry form a series intermediate in their habits of bearing 
between the peach on the one hand and the sweet cherry on the other. 
That is, all of these fruits bear fruit-buds laterally on both long and short 
growths. Some of them, as certain of the almonds and Japanese plums, 
approach the peach more closely; others, as the Insititia plums, approach 
the sweet cherry more closely. The age and vigor of the trees and the 
cultural conditions under which they are grown influence the relative 
distribution of fruit buds on spurs and on shoots. Roberts 43 states that 
weak or moderately vigorous sour cherry trees bear a much larger per- 
centage of their fruit buds on medium to short shoots than do the vigorous 
trees of the same varieties. The reverse is likely to hold in certain varie- 
ties of the Japanese plum. 

Since the bearing habits of these fruits are intermediate between 
those of the peach and of the sweet cherry, it follows that their pruning 
treatments should likewise be intermediate between those given typical 
bearing trees of those species. If the bearing habit is more like that 

30 



466 FUNDAMENTALS OF FRUIT PRODUCTION 

of the peach the pruning treatment should be correspondingly severe; 
if it is more like that of the sweet cherry it should be correspondingly light. 
In kind, likewise, it should resemble that of the fruit whose bearing habit 
it most closely resembles. Furthermore, with a change in the bearing 
habit as the tree grows older or as its environment varies there should be a 
corresponding change in the amount and kind of pruning. 

In general with these fruits it is usually desirable to employ those 
cultural and pruning practices that encourage the spur-bearing, rather 
than the shoot-bearing, habit. The production of fruits on spurs means 
compactness of trees, less danger from the breaking of limbs and lighter 
and less expensive pruning. There is not the necessity of constant prun- 
ing for "renewal" purposes. It has been found in the sour cherry at 
least that spur-borne fruit buds are hardier than those borne on shoots. 43 

Pruning the Currant and Gooseberry. — The fruiting habits of the 
currant and the gooseberry resemble that of the apricot more closely than 
those of any of the other tree fruits. Within certain limits their pruning 
treatment should follow closely that found best suited to the apricot. 
Since the currant and gooseberry are bush, rather than tree, fruits, they 
have a marked tendency to throw out strong vigorous new shoots from 
the crown or from the base of the old canes. The growth of this wood, 
together with fruiting of the older wood, weakens the latter and a point 
is soon reached where its retention is no longer profitable. Experience 
has demonstrated that canes more than four years old should be removed 
to make room for the younger and more vigorous growth. As a rule more 
new shoots form each season than can be retained without undue crowd- 
ing. Consequently they are thinned each spring to from 3 to 6 of the 
strongest and best distributed; these are headed back to a height of 
2 or 3 feet to keep the bush more compact. Thus, when the currant 
or gooseberry plantation once becomes well established, its annual 
pruning actually comprises a removal of the old canes that are becoming 
weak and a thinning of the new shoots to make provision for the replacing 
of the old wood that is discarded. Injured or diseased canes are of 
course removed and some attention should be devoted to training. 

Certain varieties or types that have growing or fruiting habits 
different from those described as typical should receive a correspondingly 
different pruning treatment. The wood of the black currant loses its 
vigor and becomes relatively unproductive at an earlier age than that of 
the red currant or the gooseberry. Consequently the old canes are 
removed after they have fruited 1 or 2 years and a correspondingly larger 
number of new shoots are retained each season for replacement purposes. 

Both currants and gooseberries may be trained in either the bush or 
the tree form. In America the bush form is preferable, both because 
less labor is required in training and because it lends itself more readily 
to an economical control of the currant borer. 



PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 467 

Pruning the Brambles. — Most of the bramble fruits are perennials, 
with biennial canes. The dying of the canes at the end of their fruiting 
season the second year necessitates their removal. Experience demon- 
strates that it is good practice to cut out and destroy the old canes 
promptly after the fruiting season. Their retention until the following 
fall or spring can serve no useful purpose and they prove a source for the 
spread of diseases and insects to the new growth if they are allowed to 
remain. 

The early spring pruning of this group usually consists in some thin- 
ning out of the cane growth that is to bear fruit during the following 
summer and at the same time a heading back of the main canes or of their 
laterals, or perhaps of both. This pruning is done almost exclusively for 
the purpose of thinning the crop. If done properly it reduces the number 
of fruit buds but results in little or no reduction in the total yield. Natur- 
ally its severity varies greatly with variety and with the environmental 
conditions. The moisture supply during the ripening season limits yield 
in the bramble fruits probably more frequently than any other single 
factor. Consequently the severity of the pruning should be influenced by 
the prospect for available water during and just before harvesting. 
Under conditions of ample rainfall or abundant irrigation water and of 
relatively high atmospheric humidity this pruning may be much less 
severe than when summer drought is likely. The bulk of this spring 
pruning of dormant or nearly dormant canes should consist in heading 
back rather than in thinning out. The laterals from the median and 
more basal fruit buds generally produce larger clusters and their indi- 
vidual berries are larger than those from the more apical buds. It is a 
good plan to delay this pruning until the buds are swelling in the spring so 
that the winter-injured ends of the canes may be removed without extra 
labor. 

The summer pinching of the bramble fruits has been discussed under 
the heading of Pinching and need not be treated at this point. 

Few or no data are available showing the best methods of pruning 
certain types of the blackberry that have perennial canes. However, 
observation indicates that they can be handled best by treating them as 
ordinary varieties with biennial canes. That is, their canes are pruned 
out as soon as they have fruited once, even though they would bear a 
second crop were they allowed to remain. 

The so-called everbearing or fall-bearing raspberries produce their 
late summer crop terminally on the main shoot or on sub-terminal laterals 
of shoots of the current season. The following main-season crop is 
borne on laterals coming from lower parts of the same canes. They 
should be winter pruned in the same way as related mid-season varieties. 

Pruning the Grape. — More has been written about pruning and 
training the grape than any other fruit, Many different systems or 



468 FUNDAMENTALS OF FRUIT PRODUCTION 

methods have been worked out and described in detail and an examina- 
tion of any considerable part of this literature is as likely to be confusing 
as it is enlightening. This is not because the several practices differ so 
much in the principles involved, but because there is so great diversity in 
the methods of their application that the principles themselves are 
likely to remain hidden. 

As pointed out in the classification of bearing habits, the grape pro- 
duces its fruit buds laterally on shoots, which at the close of the growing 
season and for a year thereafter are called canes. These fruit buds give 
rise to flower-bearing or fruiting shoots on which the inflorescences appear 
to be lateral. However, many shoots form few or no fruit buds, particu- 
larly those springing from latent or adventitious buds on 2-year-old 
or older wood — in other words, those arising from the arms, head, trunk 
or crown of the plant. Only those shoots (canes, when a year old) coming 
from lateral buds on the canes of the preceding season are sure to form 
fruit buds, though under some conditions those coming from the older 
wood differentiate a limited number. Furthermore not all buds on shoots 
springing from the preceding year's canes contain flower parts. Those 
at the basal one to four or five nodes, depending largely on variety, seldom 
do. Though it is difficult, and often impossible, to distinguish the fruit 
buds from the leaf or wood buds by their external appearance, their 
position on the plant offers a rather accurate index to their character 
and the grower or student, once he becomes well acquainted with the 
characteristics of the individual variety, will have little difficulty in telling 
which are of the one kind and which of the other. 

Severity of Pruning. — Practically all grape vines differentiate each 
year more fruit buds than can grow into fruiting shoots and set and mature 
grapes the following season. It is therefore unnecessary in pruning the 
grape to give thought to securing larger numbers of fruit buds. The real 
problem is that of reducing to just the right number those that are already 
formed and normally would or could produce fruiting shoots the following 
season. Furthermore, this must be done in such a way that the fruit 
will be well distributed and that the new shoots on which fruit buds for a 
succeeding crop are differentiated will be so located as to preserve the 
compactness and established form of the vine. 

The reduction of fruit buds to just the right number is often difficult 
and always requires an accurate knowledge of fruit-bud location in the 
particular variety and good judgment as to how much fruit the vine 
should bear. Overpruning reduces the crop and diverts the energies of 
the plant into excessive wood growth. This is well illustrated by the 
work of Maney 34 in Iowa. Underpinning permits the plant to overbear, 
resulting in too many clusters, undersized berries of inferior quality and a 
Weakening of the vine itself so that succeeding crops will be reduced in 
size and the life of the plant shortened. These statements, of course, 



PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 469 

apply to the pruning of many other fruit plants, but not to the same 
extent that they do to the grape. In practice perhaps the best way of 
determining the severity of pruning is, following a suggestion of Hed- 
rick, 26 to figure the problem for each vine on a mathematical basis. He 
says in reference to varieties of the Labrusca and Labrusca-hybrid types: 
"A thrifty grape-vine should yield, let us say, 15 pounds of grapes, a 
fair average for the mainstay varieties. Each bunch will weigh from 
a quarter to a half pound. To produce 15 pounds on a vine, therefore, 
will require from 30 to 60 bunches. As each shoot will bear two or three 
bunches, from 15 to 30 buds must be left on the canes of the preceding 
year. . . . Pruning, then, consists in calculating the number of bunches 
and buds necessary and removing the remainder." As some of the fruit- 
ing shoots may be broken off incident to the work of cultivation, spraying 
or other vineyard operations, it may be well to leave a few extra fruit 
buds; this matter, however, can be overdone easily. 

Special mention should be made of the variation in the relative 
amounts of pruning to be given vines of any given variety, not only with 
their age and the conditions of soil moisture and fertility but, in grafted 
vines, with the stocks on which they are grown. Certain stocks have the 
reputation of producing shy-bearing vines, though actually they are 
unproductive only when pruned too closely. 

Another point already mentioned is the provision that should be made 
for the production of properly placed new shoots on which fruit buds for 
the following crop can form. In practice this "proper distribution" 
generally involves their location as near the head of the vine as possible, 
so that the fruiting wood is not pushed out unnecessarily each season; 
thus the plant is kept compact. In many varieties this is secured by 
retaining the lowest or basal cane (fruiting shoot of the preceding season) 
on each arm or spur and pruning away those originating farther from the 
head. In certain other varieties, however, the fruiting shoots develop 
only from buds at nodes some distance from the base of the canes and the 
more basal buds remain dormant when the heading back is light enough 
to permit the development of fruiting shoots. Pruning varieties with 
such growing and fruiting habits in the way just described would quickly 
carry the bearing surface of the vine far from its head and necessitate 
frequent resort to pruning like that called dehorning in tree fruits. The 
usual method of handling vines of this type is each year to prune lightly 
or moderately certain canes for fruit production, leaving them with the 
requisite number of fruit buds and to prune severely other canes so that 
all their fruit buds are removed and they are forced to develop vegetative 
shoots from their basal buds. These vegetative shoots then become the 
fruiting canes of the following year, while those that have borne fruit 
are entirely removed. These much shortened canes are spoken of as 
"renewal spurs." 



470 FUNDAMENTALS OF FRUIT PRODUCTION 

Kind of Pruning. — Pruning the grape, like the pruning of most other 
fruits, includes some thinning out and some heading back. The relative 
amounts of these two types desirable in any given case depend largely on 
the style of training employed. Invariably all the past season's shoots 
are removed except those retained for their fruit buds or for "renewal" 
or "replacement." This is a thinning out process. If the style of train- 
ing calls for pruning to spurs, more of last season's shoots must be 
retained; consequently there can be less thinning out than if the vines are 
pruned to canes. As the pruning should leave a fairly definite number of 
fruit buds, the amount of heading back of the canes left after thinning 
varies inversely with their number. Thus there is much less severe 
heading with a two-wire Kniffin system of training than with pruning 
back to spurs. Little need be said at this point regarding the summer 
pruning of the grape, as the more important features are discussed in 
Chap. XXIV. 

Methods of Training. — As already indicated, there is almost endless 
variety in methods of training the vine. A description of each, even of 
those that are fairly distinct, would require many pages and probably 
would be of little real use. The fundamental objects of all these methods 
differ little from those governing the training of other fruit-producing 
species. Training should increase yields, improve grades or quality and 
reduce production costs through facilitating other vineyard operations. 
In this fruit the usual training methods, at least those employed in 
America, have little influence on total yields. 24 They do, however, affect 
quality and production costs. No one method of training is necessary 
for the production of fruit of the highest grade or quality. Thus in New 
York, vines of the Concord have been found to mature their fruit better 
when trained to the umbrella Kniffin system than when trained in any of 
the other ways standard in that state. 24 Husmann and Dearing 30 report 
that in Muscadine grapes the upright system permits the fruit to ripen 
more evenly than does the overhead system. Only after a careful study 
of the growing and fruiting characteristics of the different varieties in 
various sections and soils and on different stocks can the best system 
of training be selected and the best system for one variety may not be best 
for another in the same vineyard. 

In general those systems of training in which the new shoots are 
allowed to droop are much less costly than those in which they are tied 
in horizontal or vertical positions; consequently it is only under special 
conditions that these latter methods of training are to be recommended. 
Along the northern limits of outdoor grape culture some of the low renewal 
systems of training greatly facilitate the work incident to artificial 
winter protection and are quite generally employed. Those varieties 
whose canes bear fruit buds almost to the very base, are naturally better 
suited to Spur renewal than those whose canes habitually form only 



PRUNING 471 

wood buds in the same regions. With these latter cane renewal or a 
combination of long and short spur renewal is more practicable. Only 
those varieties (particularly of the Vinifera group) with comparatively 
stocky and rigid trunks that require no artificial supports can be trained 
to the tree form advantageously. Other varieties require trellising. 

Suggested Collateral Readings 

Howe, G. H. The Effect of Various Dressings on Pruning Wounds of Fruit Trees. 

N. Y. Agr. Exp. Sta. Bui. 396. 1915. 
Roberts, R. H. Prune the Cherry Trees. Wis. Agr. Exp. Sta. Bui. 298. 1919. 
Tufts, W. P. Pruning Young Deciduous Fruit Trees. Cal. Agr. Exp. Sta. Bui. 313. 

1919. 
Alderman, W. H., and Auchter, C. E. The Apple as Affected by Varying Degrees of 

Dormant and Seasonal Pruning. W. Va. Agr. Exp. Sta. Bui. 158. 1916. 
Gardner, V. R., Magness, J. R., and Yeager, A. F. Pruning Investigations. Ore. 

Agr. Exp. Sta. Bui. 139. 1916. 
Magness, J. R., Edminster, A. F., and Gardner, V. R. Pruning Investigations. 

Ore. Agr. Exp. Sta. Bui. 146. 1917. 
Bioletti, F. T. Vine Pruning in California. Cal. Agr. Exp. Sta. Bui. 241. Part 1. 

(No date.) 
Drinkard, A. W. Fruit Bud Formation and Development. Ann. Rept. Va. Agr. 

Exp. Sta. Pp. 159-205. 1909-10. 
Sorauer, P. A Popular Treatise on the Physiology of Plants. Transl. by F. E. 

Weiss. Pp. 134-168. London, 1895. 
Bioletti, F. T. Vine Pruning in California. Cal. Agr. Exp. Sta. Bui. 246. Part 2. 

1914. 

Literature Cited 

1. Alderman, W. H., and Auchter, E. C. W. Va. Agr. Exp. Sta. Bui. 158. 1916. 

2. Barry, P. The Fruit Garden. Pp. 94-95. Detroit, 1853. 

3. Batchelor, L. D., and Goodspeed, W. E. Utah Agr. Exp. Sta. Bui. 140. 1915. 

4. Bedford, H. A. R., and Pickering, S. U. Science and Fruit Growing. Pp. 57-80. 

London, 1919. 

5. Ibid. P. 46. 

6. Bioletti, F. T. Cal. Agr. Exp. Sta. Bui. 241. 1913. 

7. Blake, M. A., and Connors, C. H. N. J. Agr. Exp. Sta. Bui. 326. 1917. 

8. Brierley, W. G. Proc. Am. Soc. Hort. Sci. 16: 102-104. 1919. 

9. Card, F. W. Bush Fruits. Pp. 48-51; 70-73. New York, 1917. 

10. Chandler, W. H. Mo. Agr. Exp. Sta. Res. Bui. 14. 1914. 

11. Chandler, W. H. Proc. Am. Soc. Hort. Sci. 16: 88-101. 1919. 

12. ChQds, L. Ore. Agr. Exp. Sta. Bui. 171. 1920. 

13. Cole, S. W. The American Fruit Book. P. 57. Boston, 1850. 

14. Curtis, O. F. Am. J. Bot. 7: 101-124. 1920. 

15. Daniel, L. Compt. rend. 131:1253-1255. 1900. 

16. Daniel, L. Trav. scient. Univ. de Rennes. 6 (2) : 22-72. 1907. 

17. Downing, A. J. The Fruits and Fruit Trees of America. P. 31. New York, 

1856. 

18. Drinkard, A. W. Va. Agr. Exp. Sta. Ann. Rept. Pp. 96-120. 1913-1194. 

19. Drinkard, A. W. Va. Agr. Exp. Sta. Tech. Bui. 17. 1917. 



472 FUNDAMENTALS OF FRUIT PRODUCTION 

20. Edminster, A. F. Ore. Agr. Exp. Sta. Bui. 146. 1917. 

21. Gardner, V. R., et al. Ore. Agr. Exp. Sta. Bui. 139. 1916. 

22. Gardner, V. R. Ore. Agr. Exp. Sta. Bui. 146. 1917. 

23. Gaucher, N. Handb. der Obstkultur. Pp. 602-644. Berlin, 1902. 

24. Gladwin, F. E. N. Y. Agr. Exp. Sta. Bui. 464, 1919. 

25. Goumy, E. Thesis Presented to the Faculty of Science of the University of Paris. 

1905. 

26. Hedrick, U. P. Manual of American Grape Growing. P. 114. New York, 

1919. 

27. Hovey, C. M. Hovey's Mag. of Hort. 15: 301. 1849. 

28. Howe, G. H. N. Y. Agr. Exp. Sta. Bui. 391. 1914. 

29. Husmann, G. C. U. S. D. A. Bui. 856. 1920. 

30. Husmann, G. C, and Dearing, C. U. S. D. A., Bur. PI. Ind. Bui. 273. 1913. 

31. Macoun, W. T. Can. Dept. Agr. Bui. 56. 1907. 

32. Magness, J. R. Ore. Agr. Exp. Sta. Bui. 139. 1916. 

33. Magness, J. R. et al. Ore. Agr. Exp. Sta. Bui. 146. 1917. 

34. Maney, T. J. la. Agr. Exp. Sta. Bui. 160. 1915. 

35. Paddock, W. N. Y. Agr. Exp. Sta. Bui. 151. 1898. 

36. Paddock, W., and Whipple, O. B. Fruit Growing in Arid Regions. P. 112. 

New York, 1910. 

37. Pearson, A. H. J. Roy. Hort. Soc. 29: 274. 1896. 

38. Quinn, P. T. Pear Culture for Profit. P. 72. New York, 1889. 

39. Quintinye, J. de la. Instructions pour les jardins fruitiers et potagers. 2: 579. 

Paris, 1746. 

40. Ravaz, L. Taille hative ou taille tardive. 1912. (Cited by Bioletti, F. T., 

Cal. Agr. Exp. Sta. Bui. 241. 1913.) 

41. Rivers, T. The Miniature Fruit Garden. P. 8. New York, 1866. 

42. Ibid. Pp. 12, 82. 

43. Roberts, R. H. Wis. Agr. Exp. Sta. Bui. 298. 1919. 

44. Roberts, R. H. Wis. Agr. Exp. Sta. Bui. 317. 1920. 

45. Taft, L. R., and Lyon, T. T. Mich. Agr. Exp. Sta. Bui. 169. 1899. 

46. Thomas, J. J. American Fruit Culturist. P. 82. New York, 1867. 

47. Tufts, W. P. Cal. Agr. Exp. Sta. Bui. 313. 1919. 

48. Vidal, J. L. Rev. de Viticulture. 1:895-903. 1894. 

49. Vincent, C. C. Ida. Agr. Exp. Sta. Bui. 98. 1917. 

50. Volck, W. H. Mo. Bui. Cal. St. Com. Hort. 6: 80-89. 1917. 

51. Waugh, F. A. The American Apple Orchard. P. 90. New York, 1912. 

52. Yeager, A. F. Ore. Agr. Exp. Sta. Bui. 139. 1916. 









SECTION V 
FRUIT SETTING 

It is customary to speak of the reproductive activities of the plant ■ 
as distinct from its vegetative activities. That use of terms is accepted 
and followed here, though it is not always an easy matter to define the 
two. The woody tissues of the shoot and spur may by common consent 
be considered vegetative in character. Likewise, it is generally agreed 
that the ovarian tissues of the fruit may be classed as reproductive, 
being more intimately associated with reproduction than with vegetative 
growth. On the other hand, there might easily be some difference in 
opinion regarding the tissues composing the peduncle or central axis of the 
inflorescence. In many plants these structures differ but little from 
other stem structures and they are vegetative in character. On the 
other hand, when these tissues become fleshy and form an integral part 
of the developing fruit, as they do in the pineapple, fig and many other 
fruits, they would as naturally be considered along with the ovarian 
tissues with which they are so closely associated. Mention is made of 
these points to emphasize the fact that the problem of fruit setting is not 
necessarily limited to a consideration of strictly reproductive tissues 
and reproductive activities. Indeed, the formation of an abscission layer 
at the base of the ovary, the pedicel or the peduncle is a function of the 
sporophytic tissue at that point. Consequently it is subject to the same 
influences, though perhaps not to the same extent or in exactly the same 
way, as abscission layers developed in other places. However, fruit 
setting and fruit formation depend on the initiation and successful 
completion of at least some of the reproductory processes. Therefore, 
the more important of the processes more or less directly concerned with 
the setting of fruit are outlined briefly. 

In the great majority of higher plants, fruit and seed formation are 
conditioned on the bringing together and fusion of two specialized cells 
known as gametes. The larger of these cells is called the egg and is 
borne in the embryo sac. The smaller gametes are formed by a divi- 
sion of the generative nucleus of the pollen grain. The flower is the 
special organ of the plant for the production of these gametes. More 
specifically the stamen or microsporangium is the organ for the pro- 
duction of the male gametes and the ovule or macrosporangium the 
organ for the production of the female gametes. The great diversity 

473 



474 



FUNDAMENTALS OF FRUIT PRODUCTION 



in the size, form, color and odor of flowers does not modify the funda- 
mental processes which take place, following pollination, in the growth of 
the pollen tube or in fertilization. In this discussion, therefore, but 
little attention need be given to the structure of the so-called non- 
essential flower organs. 




Plate I. — Successive stages in the development of the ovule of the orange. In Figure 
1, mm = macrospore, ii = inner integument, and oi = outer integument. Figs. 2 and 3, 
later stages in which the integument more nearly encloses the nucellus. Fig. 4, the fully 
developed embryo sac, showing the egg apparatus at the upper end, the polar bodies near 
the center, the antipodals at the bottom. Fig. 5, the embryo sac after fertilization, one 
of the synergids (pt) disintegrating, the egg cell at oo, and 8 endosperm nuclei (en). (After 



Osc 



°) 



CHAPTER XXVI 

THE STRUCTURES AND PROCESSES CONCERNED IN FRUIT 

FORMATION 

The entire flower may be regarded as a specialized branch, consisting 
of a central axis to which are attached several whorls or sets of organs 
that bear a certain resemblance to leaves. The two outer or lower 
whorls, the calyx and corolla, take no direct part in reproduction and 
are spoken of as non-essential organs, though after fertilization the 
calyx may undergo considerable differentiation and form a considerable 
part of the mature fruit. As stated before, the stamens bear the male 
gametes. In the higher plants, exclusive of the gymnosperms, the female 
gametes are developed inside an enclosed structure, the ovary. This 
last may consist of a single carpel (or modified leaf, to follow the concep- 
tion of one school of botanists) or of several that are more or less com- 
pletely united. In the latter case the ovary and the fruit which develops 
from it, may be several-loculed. That portion of the central axis of the 
flower to which the several sets of floral organs are attached is the recep- 
tacle or torus. 

A fruit may be defined as a ripened ovary together with whatever 
may be intimately attached to it at maturity. If it consists of a ripened 
ovary only, as in the peach or tomato, it is a simple fruit; if it includes 
additional structures it is spoken of as an accessory fruit. Sometimes 
the accessory structure may be the torus, as in the apple; sometimes 
the torus and the calyx, as in the cranberry and sometimes a part of 
the peduncle or pedicel, as in some varieties of the pear. The developing 
ovaries of certain fruits grow together and give rise (1) to aggregate 
fruits, if they all belonged to the same flower, as in the raspberry, or 
(2) to multiple fruits if they belonged to different flowers, as in the 
mulberry. In the latter the mature fruit includes ovarian, toral and 
stem tissues. Not infrequently the ovarian tissues constitute only a 
small part of the mature fruit and as a rule it is the accessory tissues 
(when they are present) in which the pomologist is mainly interested, 
for they are likely to constitute most of its edible portion. However, 
it is the ovary with its enclosed ovules on which fruit formation 
depends; consequently a discussion of fruit setting and fruit formation 
must start with the ovary and its ovules. 

The Ovule. — The ovule arises as a protuberance from the inner wall 
of the ovary. The particular points, lines or surfaces from which it 

475 



476 



FUNDAMENTALS OF FRUIT PRODUCTION 




/^-> 










Plate II. — Successive stages in the development of the pollen grain of the grape. 
Fig. 1, section of anther showing epidermal, middle, tapetal and mother-cell layers. Figs. 
2 and 3, later stages in these same layers. Fig. 4, a pollen-mother-cell. Fig. 5, the tetrad 
stage in the pollen-mother-cell. Fig. 6, a microspore or pollen grain, before its liberation 
from the pollen-mother-cell. Fig. 7, a pollen grain of the Concord grape. Fig. 8, the genera- 
tive cell in a mature pollen grain. Figs. 9-12, various stages in the development of the 
generative and vegetative nuclei, but in each instance one or both nuclei are undergoing 
degeneration. Fig. 13, the normal generative cell and vegetative nucleus of a pollen grain. 
(After Dorsey. 36 ) 






FRUIT FORMATION 477 

springs are known as the placentae. Successive stages in the develop- 
ment of a typical ovule are shown in Figs. 1 to 3 of Plate I. The ovules 
of different species vary greatly in size, shape and degree of development 
and differentiation. However, practically all differentiate into a central 
portion and one or two enveloping layers. The central portion is known 
as the nucellus, the enveloping layers as the outer and inner integuments. 
These several structures are clearly shown in Figs. 2 and 3 of Plate I. 
The integuments never completely enclose the nucellus but leave an 
opening of varying size, the micropyle, through which the pollen tube 
usually passes to effect fertilization. The stalk or filament by which the 
ovule is attached to the ovarian wall is known as the funicle. Through 
it the ovule and later the developing seed receives its supply of food 
material. In many species the funicle is fused with the outer integument 
for a short distance, giving rise to a ridge known as the raphe. The 
point where the nucellar and integumental tissues are continuous and 
grown together is the chalaza. 

The Embryo Sac. — At an early stage in the development of the 
nucellus, one of its cells, the macrospore, becomes differentiated from 
the others. This cell enlarges and divides first into two and then into 
four cells forming the axial row. The first division of the macrospore 
mother cell is the reduction division, which means that the number 
of chromosomes in the nucleus of each of these four cells is half of the 
number in the mother cell from which they were derived. Ordinarily 
only one of these four cells develops and this becomes the embryo sac, 
shown in Fig. 3 of Plate I. Its nucleus divides into two, then four and 
finally eight, presenting the condition shown in Fig. 4 of Plate I. At this 
stage the protoplasm of the embryo sac is highly vacuolated. At one 
end, three of the nuclei are visible, constituting the egg apparatus. Only 
one is capable of being fertilized. The other two are called synergids; 
their exact function is not known. At the opposite end of the embryo sac 
are three nuclei called antipodals which are separated at an early stage 
from the rest of the sac contents by the formation of cell walls. These 
cells do not take any direct part in the process of fertilization and they 
do not influence the development of the fruit so far as known. Sooner 
or later they, like the synergids, disintegrate. Near the center of the 
embryo sac are the other two nuclei called polar bodies because each has 
come from the group of nuclei at the extreme ends or poles of the embryo 
sac. These nuclei fuse and divide rapidly, forming the endosperm; in 
many instances one of the male gametes unites with the fusion nucleus 
bringing about double fertilization. 

Pollen. — Stamens originate as small protuberances at their points 
of insertion on the axis of the flower. At first these projections consist 
of homogeneous tissue, but differentiation soon occurs and it becomes 
possible to recognize filament and anther. The anther increases in 



478 FUNDAMENTALS OF FRUIT PRODUCTION 

size more rapidly than the filament and gives rise to a structure that is 
generally grooved longitudinally on the outside and four-loculed in 
cross section. Figures 1 to 8 of Plate II show successive stages in the 
development of the male reproductive cell, or pollen grain, from the 
tissues of the anther in the grape. At a comparatively early stage there 
is a differentiation between the cells of its outer layers and those in the 
interior. This differentiation has progressed rather far in the section 
shown in Fig. 1, Plate II, the epidermal, middle, tapetal and mother- 
cell layers being clearly distinguishable. Eventually the epidermal 
and sub-epidermal layers undergo a series of changes which lead to 
their separation from the sporogenous tissue within and to their assuming 
the role of a simple protective shell or covering. Some idea of these 
changes is afforded by Figs. 2 and 3 of Plate II. Figure 4 of Plate II 
shows a single large pollen-mother-cell just previous to the reduction 
division, which gives rise to four daughter cells, each of which is sur- 
rounded by a membrane or cell wall. This is the so-called tetrad stage, 
shown in Fig. 5, Plate II, though only three of the four microspores are 
shown in the plane in which that figure was drawn. Shortly after the 
formation of these tetrads the mother-cell wall breaks down and liberates 
the microspores. Figure 6 of Plate II shows one of the microspores of the 
Brighton grape just previous to its liberation and Fig. 7 of Plate II shows 
one of the Concord variety a short time after its liberation. Its thick 
wall, large nucleus and vacuole are prominent. Usually some time 
before, though sometimes after, the dehiscence of the anther and the 
dispersal of the pollen there are further changes within the pollen grain. 
The nucleus divides giving rise to two daughter nuclei. One is called the 
generative nucleus, because it alone gives rise to the gametes. This 
generative nucleus becomes surrounded by a cell wall and is then called 
the generative cell of the pollen grain. The other is called the vegetative 
nucleus, because its function is more closely associated with germination 
and because it functions as the nucleus of the pollen tube. Figures 9 
and 12 of Plate II show two stages in the development of these two nuclei, 
though both cases are somewhat abnormal because they show the initial 
stages of a degeneration that leads to impotency. Figure 14 of Plate II 
shows the generative cell and vegetative nucleus of a mature pollen grain 
of the Concord grape before dehiscence. 

Pollination. — In the ordinary course of events the maturing of the 
ovules and of the pollen grains is followed by a transfer of pollen from 
stamen to stigma. If the transfer is from stamen to stigma of the same 
flower or to the stigma of another flower on the same plant, or, in the 
case of pomological varieties, to the stigma of a flower on any plant of 
the same variety, the process is self pollination. If the transfer is to 
the flower of another individual, or, in the case of pomological varieties, 
to the flower of another variety, the process in cross pollination. When 



FRUIT FORMATION 



479 




Plate III. — Fig. 1, an early stage in the development of the normal orange embryo, 
showing the so-called suspensor. Figs. 2-4, stages in the development of the ovule of the 
orange showing various degenerative changes which result in embryo abortion; should the 
fruit mature it would be seedless. {After Osawa. 100 ) 



480 FUNDAMENTALS OF FRUIT PRODUCTION 

self pollination is effected without the aid of any outside agency, such 
as wind or insects, the process is known as autogamy. Many of the 
peculiarities of form, structure, color and odor of flowers are closely 
associated with means for securing proper self or cross pollination. 
Some of the factors which are of importance in aiding or preventing 
pollination are discussed later. 

Germination of the Pollen Grain. — Pollination is usually followed 
promptly by the germination of the pollen grain. This is brought 
about by the absorption of water and various substances in the stigmatie 
fluid. The grain swells and a tube is pushed out through one of the 
pores in the outer covering or extine. The tube is formed by the intine 
or inner covering which pushes out through the germ pore. As it elongates 
it penetrates the tissues of the style by growing between the cells and as it 
advances toward the ovarian cavity its rate of growth may increase. The 
styles of the flowers of many species contain rows of cells that may be 
looked upon as specialized conducting tissue for the purpose of guiding and 
facilitating the growth of the pollen tubes. In other species there is 
no evidence of such tissue. For the most part pollen tubes digest their 
way as they go, by the secretion of a pectin-digesting enzyme. This 
dissolves the middle lamella which is composed of pectin-like substances 
that hold adjoining cells together and thus permits the insertion of the 
pollen tube between them. 103 Green 57 has shown that the pollen 
of many kinds of plants contains diastase and some kinds were found to 
contain invertase as well; during the process of germination these enzymes 
increase in amount. Presumably they are effective in rendering available, 
for the nutrition of the pollen tube, food materials stored in either pollen 
grain or style. This assumption is supported by work which showed that 
pollination produces a rapid rise of respiratory activity in the gynaeceum. U1 

In Pelargonium zonale the amount of carbon dioxide produced by 
the pollinated flowers is 5.8 times greater than that produced by the 
unpollinated flowers, though most other cases studied were somewhat 
less extreme. It was also found that in every case pollination resulted 
in some change in the respiratory coefficient — the ratio of oxygen taken 
in to the carbon dioxide given off. 

Course of the Pollen Tube. — For the most part, the growth of the pollen 
tube is directed by chemotropic influences supplied by the tissues of 
the ovary, the ovules and by the style and stigma. Miyoshi 94 sowed 
pollen grains on agar in which were imbedded pieces of stigma, ovary 
and ovules of different degrees of development. The pollen tubes grew 
toward the pieces from the vicinity of the stigma, but they were attracted 
most strongly by ovules ready for fertilization, growing into the micropyle 
in each instance. In other investigations pieces of stigmatie tissue were 
observed to influence the direction of pollen tube growth at distances 
up to 70 times the diameter of the pollen grain. 76 Pollen tubes are 



FRUIT FORMATION 481 

especially sensitive to sugar solutions, growing toward them readily. 
They tend to grow away from dry air and "show a preference for spaces 
saturated with aqueous vapour to such as are less humid." 76 Investi- 
gations of the mode of growth of the pollen tube in Houstonia led to the 
conclusion that the tissues of the style influence its direction only in a 
passive manner but that "a chemotactic stimulus originating in the 
egg-apparatus, or the egg itself, is the chief directive influence." 91 
Dorsey, however, has found tubes growing in plum styles with aborted 
ovules; therefore it is possible that growth often depends less on a 
normal egg-apparatus than the work with Houstonia would indicate. 
Dorsey found also that in the apple the pollen tube may grow beyond 
the ovule and down into the stem. Kerner and Oliver 76 state that 
ovules ready for fertilization "attract not only pollen-tubes from pollen 
of the same species, but of others far removed from it in point of affinity. 
The delicate hyphae of several mould-fungi are similarly attracted." 

Time for Pollen Tube Growth. — Ordinarily germination of the pollen 
grain occurs promptly after pollination, the pollen tube grows fairly 
rapidly and fertilization occurs within a period of 1 or 2 days, though 
the time may be expected to vary with temperature and other environ- 
mental factors. Under favorable conditions there is an interval of from 
9 to 120 hours between pollination and fertilization in apples, plums 
and cherries. 114 ' 84 The very much slower growth of Rome pollen tubes in 
Rome styles as compared with that of the tubes of other apple varieties 
found by one investigator 84 is interesting and may offer an explanation of 
some cases of self sterility. A period of from 26 to 41 hours has been re- 
ported in the case of certain cucurbitaceous plants, 83 4 days in one of the 
species of Gastrodia, 87 one month in Betula, 6 several months in Hamamelis 11 6 
and approximately a year in certain of the oaks. 22 That there may be 
a great variation in this respect between closely related plants is evident 
from the behavior of the Satsuma orange in which about 30 hours have 
been found to elapse between pollination and fertilization, 18 while a 
corresponding period of 4 weeks has been reported in Citrus trifoliata. 100 

Fertilization. — In Fig. 13 of Plate II are shown the vegetative 
nucleus and the generative cell of the mature pollen grain. During the 
growth of the pollen tube the nucleus of the generative cell divides, giving 
rise to two male gametes, each consisting of a nucleus and a small portion 
of stainable material. The pollen tube, after entering the micropyle, 
penetrates the intervening tissue of the nucellus and then enters the 
embryo sac. The following account of fertilization is adapted from 
Mottier's 95 description of the process: The end of the tube may enter 
the sac at one side of the synergids, in which case only one of these cells 
is at once disorganized, the other retaining its normal structure for some 
time. This condition is illustrated in Fig. 5, Plate I. Often it enters 
between the two synergids, in which case both cells disintegrate almost 



.482 FUNDAMENTALS OF FRUIT PRODUCTION 

immediately. "As soon as the end of the pollen tube enters the embryo- 
sac it opens, discharging the two male gametes and other contents. One 
of the male nuclei enters the egg-cell and applies itself to the nucleus of 
the egg, while the other passes into the cavity of the sac. ... It is pre- 
sumably the first male nucleus which escapes from the pollen tube that 
unites with the nucleus of the egg, but positive proof on this point is 
wanting. ... As fusion progresses, the nuclei become quite alike in 
shape, size and structure. Their membranes gradually disappear at the 
place of contact, their cavities become one, and the resulting fusion 
nucleus, which is in the resting condition, can scarcely be distinguished 
from the nucleus of an unfecundated egg. The nucleoli finally unite 
also." The fertilized egg cell becomes the embryo cell, the antecedent 
of the embryo. 

Secondary Fertilization. — Attention has been called to the presence 
of two nuclei, the so-called polar nuclei, near the center of the mature 
embryo sac. These are shown clearly in Fig. 4 of Plate I. Usually these 
two fuse with the second sperm nucleus and the nucleus resulting from 
this triple fusion divides repeatedly giving rise to many daughter nuclei, 
shown in Fig. 5 of Plate I. Soon these daughter nuclei are separated by 
the formation of cell walls, the resulting tissue being the antecedent of the 
seed endosperm. 

Sometimes the second sperm nucleus fuses with but one of the polar 
nuclei 138 and sometimes it degenerates in the cytoplasm of the embryo 
sac. In the former case, the endosperm is of the same parentage as the 
embryo beside which it develops; in the latter case it is built from 
maternal tissue alone. In plants with albuminous seeds, this results in 
the condition known as xenia. 

Development of the Embryo and Endosperm. — Following the process 
of fertilization the embryo cell "divides by a transverse wall into two 
cells, one directed towards the micropyle, the other towards the base of 
the embryo sac. The upper of these two cells stretches, and is repeatedly 
segmented; thus a string of cells is formed, known as the suspensor, bear- 
ing at its lower extremity the embryo-cell, which gives rise to the greater 
portion of the young plant." 80 This stage is shown in Fig. 1, Plate III. 

Coordinate with the development of the embryo is that of the 
endosperm. To be exact, in most developing seeds the growth of the endo- 
sperm is at first more rapid than that of the embryo. In many exal- 
buminous seeds there is a period of very rapid growth of the endosperm 
during which the young embryo either grows very slowly or persists in 
a practically resting stage. This is followed by a period of rapid embryo 
development, which occurs largely at the expense of the materials accu- 
mulated in the endosperm. The initiation of this period of rapid growth 
in the slow growing or resting embryos is apparently one of the "sticking 
points" in the process of seed formation and in many species it is very 



FRUIT FORMATION 483 

important in determining whether or not the fruit shall mature or fall 
prematurely. 

In the developing seeds of most species the tissues of the nucellus 
disintegrate and their substance is used by the growing endosperm or 
embryo. In some species, however, the nucellar tissues persist and develop 
into a storage tissue that can hardly be distinguished from endosperm. 
Storage tissue of such origin is known as perisperm. 

THE SETTING OF THE FRUIT 

The fertilization process and the following segmentation and growth of 
the embryo and endosperm within the ovule are accompanied by changes 
in the surrounding ovary wall and often in the torus and other adjoining 
tissues. Most noticeable among these changes is a thickening and an 
increase in size, perhaps with some change in color, shape and position, 
so that it is evident very soon after blossoming that the fruit has or has 
not "set," or that there is or is not a possibility of its maturing properly 
in due time. 

However, some blossoms do not set fruit and sometimes the percentage 
that sets is extremely small. Nothing is of greater importance to the 
fruit grower than having a reasonable percentage of the blossoms set. 
Yield, income and profits are all absolutely dependent on what the tree 
does in this respect at and just after the time of blossoming. Of course 
accidents or unfavorable conditions later in the season may injure or 
destroy the crop, but they are contingencies with which the grower has 
greater confidence in dealing than the accidents that may befall at the 
time of fruit setting. 

The term "fruit setting" is used here to refer to the initial and appreciable 
swelling of the ovary occurring shortly after the period of petal fall. It is gener- 
ally accompanied by some thickening of the pedicel or of the peduncle. Meanwhile, 
flowers that have not " set " are turning yellow or withering and falling off. After 
this stage is passed accidents may happen and the "June drop" or some other 
"drop" or some environmental factor may cause abscission; nevertheless, at 
least for the time being, it appears as though fertilization had taken place and 
the chances are good for the fruit maturing. 

What Constitutes a Normal Set of Fruit. — It is not to be expected that 
all the blossoms will set fruit, even though conditions are ideal. In most 
species and varieties they are produced in such profusion that a total set 
would be little short of calamitous for the grower. He is more interested 
in obtaining a reasonable number of specimens of good marketable size 
than a much larger number of a size for which there is little demand. 
Furthermore, he prefers a crop such as the trees can mature without 
undue exhaustion, for then he is surer of crops the following years. 



484 FUNDAMENTALS OF FRUIT PRODUCTION 

The set that the grower would call perfect varies greatly with species, 
variety and with conditions. In 1899, Fletcher 46 counted 4725 blossoms 
of the apple, pear, plum and apricot; from these 617 fruits developed what 
was considered a full crop for the branches on which they were borne. 
It would be called a perfect set by the grower, yet the percentage actually 
setting was 13. The setting of 20 to 30 per cent of the blossoms of the 
Muscadine grape would give a full crop. 74 If, however, the setting of 10 
per cent of the blossoms provides for a full crop, a 5 per cent set will 
provide only half a crop, though proportionally but a few more blossoms 
drop. In terms of the percentage of blossoms setting, then, a difference 
of a few per cent may have a great effect on the size of the crop so that 
it becomes important to ascertain the causes of these slight differences and 
the methods of controlling them. 

The usual failure of many blossoms to set and mature fruit is due to 
many factors, the more important of which are discussed later. It 
should be understood, however, that many cultivated varieties char- 
acteristically produce more blossoms than possibly can mature into fruits 
and that consequently a certain amount of dropping is to be expected. 
This may be regarded in the same light as the nearly universal abortion 
of one of the two ovules in the ovaries of most stone fruit varieties 
or two of the three ovaries in the flower of the date palm — phenomena 
due to deep-seated hereditary causes that are quite beyond control by 
any cultural means. 

The June Drop and Other Drops. — All of the flowers that fail to 
mature fruit do not drop at one time and a continuous dropping from 
the flowering stage up to the time of maturity is not common. Instead 
there are more or less definite periods or stages when extensive dropping 
occurs. The loss comes in a series of waves, varying with the different 
fruits in number and in the length of time between them. There appear 
to be certain "sticking points," critical periods, through which each 
fruit must proceed to reach full maturity. When one of these stick- 
ing points is safely passed there is comparatively little danger of the fruit 
falling before the next critical period arrives. Apparently these sticking 
points for fruit setting are closely correlated with definite changes in 
the development taking place in the embryo and in the endosperm of the 
seeds. 

Dorsey 37 has made a careful study of dropping of blossoms and newly-set 
fruits in the plum and the following account, adapted from his report, illustrates 
the phenomenon as it occurs in fruits in general: 

The First Drop. — The first drop takes place very soon after blossoming. 
Examination of the pistils of the flowers dropping at this time shows that they 
are defective. In some, pistil abortion has occurred at an earlier stage than in 
others though the stage at which it occurs is quite constant for each variety. 
Pistils show all degrees of development, ranging from mere rudiments up to those 



FRUIT FORMATION 485 

that are nearly perfectly formed. The more defective pistils drop earliest, but 
all flowers come into full bloom. Flowers with defective pistils always drop at 
the pedicel base and neither the calyx tube nor the style is shed by abscission 
because growth is not carried far enough. The immediate cause of the dropping 
is the abortion of pistils that are structurally defective and cannot function. 

The Second Drop. — "The first drop is followed 2 weeks or so after bloom by 
another distinct wave of falling pistils. While there are a few intergrading 
forms between these two drops, certain features of the second drop separate it 
distinctly from the first. Unlike the pistils of the first drop, those of the second 
have every external appearance of being normal. Enlargement up to a certain 
point takes place and in most cases the calyx tube breaks away at least in part 
even though there is insufficient growth in the young plum to throw it off. The 
style is not deciduous in the earliest pistils to fall, but, like the calyx tube, drops 
in those which fall later. . . . Pistils which fall in the second drop, as in the 
first, absciss at the pedicel base while the pistil is still green, although the pedicel 
has become light yellow. Yet in the last pistils of the second drop to fall the 
abscission layer is formed at the base of the ovary and in some instances can 
be easily broken off at this point. . . . 

"Emphasis is placed upon the following points. . . : (a) the period of 
abscission of the second drop extended from 17 to 30 days after bloom; (b) 
beginning with the first pistils to fall, size differences between those persisting and 
those which fell, gradually increased with time; (c) pistils which fell within the 
above-mentioned time limit enlarged only up to a certain point ; (d) those pistils 
with the stigmas snipped before pollination, enlarged before falling, to a size 
comparable with that of those not so treated; and (e) in each variety there was 
a gradual increase in the size of the pistils which fell off. . . . 

"The condition found in the unfertilized series is in marked contrast with 
that found when fertilization takes place. As early as 18 days after bloom the 
embryo sac in which the egg has been fertilized extends the entire length of the 
nucellus to the chalaza, and a jacket of endosperm, usually only one cell thick, 
covers the entire area of the 'dumb-bell-shaped' sac. With the completion of 
these changes in the embryo sac the embryo may be no larger than four cells 
across. . . . 

"It will be seen from the above observations that all the evidence shows that 
fertilization has not occurred in the pistils which fall at the second drop. . . . 
Pollination may have taken place, but tube growth was retarded to such an 
extent that fertilization was prevented probably by the abscission of the style." 

The Third Drop or June Drop. — "Following the second drop there is still 
another — the so-called 'June drop.' In popular usage the term June drop 
applies primarily to the third drop of large plums because they are much more 
conspicuous, but does not include the relatively few which fall from time to time, 
even up to maturity ... It has been shown that time and size of dropping draw 
a relatively sharp line between the first and the second waves of dropping. Like- 
wise these two factors separate the second drop from the third. . . . When 
fertilization does not take place enlargement reaches only a certain point, the 
maximum recorded being in the 5.6 to 6.0 millimeter class, while the mode is 
near 3.0 millimeters. Among the last of the second drop an occasional ovule is 
found with slight embryo development, which shows that there are connecting 



486 FUNDAMENTALS OF FRUIT PRODUCTION 

forms between the second and third drops as well as between the first and second. 
In approximately one month the second drop is over, and those setting have so 
increased in size as to place them in a distinct size class from those which have 
fallen. . . . 

"Sections have been made of the embryos of a large number of plums which 
fell at the June drop. Dissections were also made of ovules at various stages to 
determine the amount of growth in the embryo. The general condition found 
may be summarized as follows: (a) embryo development started but growth 
stopped at any time from the stage when the embryo was a few cells across to 
the time at which it had reached nearly the mature size; (6) endosperm had partly 
formed, but the embryo gained the ascendency to such an extent that it was 
often found naked in the nucellus; (c) enlargement in the seed could reach nearly 
the mature size when fertilization had once occurred, accompanied by only a 
slight growth of the embryo. . . . 

"The status of development in the ovule in the third drop shows marked 
differences from that in the second. Firstly, greater size is attained than is ever 
found in the second drop, and secondly, instead of there being disintegrating 
nuclei within a slightly elongated embryo sac, tissues cease growing at various 
stages rather than disintegrating. This latter fact alone suggests an additional 
stimulus absent in the second drop. ..." 

It is not known exactly how many other fruits have three distinct 
periods in which blossoms and developing fruits drop. However, the 
sweet cherry has three such periods; some varieties, at least, of the apple 
and pear have corresponding periods and presumably they are to be found 
in a number of other fruits, though in some of these species or varieties 
they may be associated with other internal and environmental condi- 
tions. Certain other fruits, such as the currant and the raspberry 
show quite different characteristics in their fruit setting and fruit drop- 
ping. In some, as the strawberry, the flowers either set fruit or fail to set 
and there is no later dropping or abortion. However, the so-called "June 
drop," which may or may not occur in June and may correspond either to 
the second or the third drop of the plum is important in determining the 
size of the crop with most deciduous tree fruits. 

Usually, though not always, the relation between the losses incident 
to the successive drops varies with the severity of any one of them. 
Heinicke 63 points out that when the "first" drop in the apple is relatively 
large the June drop is relatively small; on the other hand the June drop 
is heavy if a comparatively large proportion of the flowers begin to form 
fruits. This may vary according to variety or with the conditions under 
which it is grown. Comparable to this is the condition pointed out by 
Reed 109 in certain lemon varieties, in which an individual flower bud on 
a small inflorescence has a greater chance to set and develop into a mature 
fruit than one on a large inflorescence. Napoleon is an example of a 
sweet cherry variety that, as grown in the Pacific northwest, almost 
invariably shows a heavy first drop, a light to heavy second drop, 



FRUIT FORMATION 487 

depending on conditions, and an almost negligible June drop. When 
Llewelling is grown under similar conditions it usually shows a fairly 
heavy first drop, a light second drop and a very heavy June drop. 

It is interesting in this connection that occasionally certain flowers 
of the cluster do not set well, while others set fruit perfectly. Schuster 115 
has called attention to this peculiarity in the flower clusters of Ettersburg 
121, a strawberry variety. The primary flowers of the cluster, those com- 
ing from the forks, set freely; only a small percentage of the secondaries, 
those coming from the lateral branches of the peduncle, set fruit. The 
case is not exactly one of blossom dropping, for the flowers do not drop 
off; but it is at least in certain respects comparable to the first drop 
described by Dorsey for the plum, though the pistils do not appear to be 
defective. Valleau 131 found in some species and in certain varieties of the 
strawberry that the later flowers to open may have sterile pistils. He 
ascribes this to a tendency toward diceciousness. 

Another interesting case of the June drop or of a phenomenon comparable 
to it is found in the date palm. Ordinarily by the end of June three partly 
grown fruits of approximately equal size have developed from the three ovaries 
of each pistillate flower. If pollination and fertilization have taken place two of 
these developing fruits drop off, leaving a single one to mature. On the other 
hand, if the flowers have not been pollinated, all three may persist and continue 
to grow slowly; they never reach full edible maturity and are without value. 
They are seedless, closely crowded together and generally somewhat deformed. 126 

Fruit Setting, Fruitfulness and Fertility Distinguished. — In the 

preceding discussion the term "fruit setting" has been used to refer both 
to the initial setting of the fruit at or just after the time of blossoming 
and to its remaining on the plant until maturity. The term is used often 
in a somewhat narrower sense to indicate whether or not it remains 
attached to the plant for any considerable time after flowering and whether 
any enlargement of the ovary takes place. Probably in the case of the 
plum just described in detail few would regard the fruit as having 
set if it did not survive the second drop, but many would consider it as 
having set if it remained through this period, even though abscission 
took place at the time of the third or June drop. There are reasons for 
refraining from an attempt to limit too closely the meaning and use of the 
term. However, it is desirable to be able to refer to definite conditions 
that are exemplified in many different species. By common consent the 
term "fruitful" is used to describe the plant that not only blossoms and 
sets fruit, but carries it through to maturity. The plant that is unable to 
do this, or that does not do it, is "unfruitful" or "barren." "Fertility" 
indicates ability not only to set and mature fruit but to develop viable 
seeds. Inability to do this is described by the terms "infertility" and 
"sterility." Fruitfulness and fertility are not synonymous, for many 



488 FUNDAMENTALS OF FRUIT PRODUCTION 

fruits, like the banana, mature their fruits though they bear no mature 
seeds. This should be emphasized because fruitful plants are often 
spoken of as being fertile, when, as a matter of fact, they may or may not 
be. Fertile plants are necessarily fruitful. Self fruitfulness, therefore, 
refers to the ability of the plant to mature fruit without the aid of pollen 
from some other flower, plant or variety, as the case may be; self fertility 
indicates a similar ability to mature viable seed without the aid of pollen 
from some other flower, plant or variety. 

Sterility and Unfruitfulness Classified. — In a general way the causes 
of sterility, unfruitfulness and of the failure of the fruit to set may be 
grouped in two main classes — those internal to the plant and those ex- 
ternal, that concern more directly its environment. Frequently it is 
difficult, if not impossible, to differentiate between these groups of 
factors, for they are interdependent to an important extent; nevertheless 
it is convenient to make such a grouping. 

Summary. — The essential organs of the flower as they concern fruit 
setting and fruit production are the pistils and stamens, though other 
parts may enter into the structure of the fruit. The changes taking 
place in the ovule and anther just previous to the time of pollination and 
fertilization are described in detail. Pollination is followed by the germi- 
nation of the pollen grain and the growth of the pollen tube, under the 
influence of chemotropic factors, down the style. With the penetration 
of the nucellus by the pollen tube and the fusion of one of the generative 
nuclei of the latter with the egg cell, fertilization is complete, though a 
secondary fertilization of one of the polar nuclei by the second generative 
nucleus occurs frequently. The embryo results from the segmentation 
and growth of the embryo cell and the endosperm is the tissue developing 
from the polar nuclei. Fertilization is usually followed by a growth of 
the surrounding ovarian tissues, resulting in a "setting" of the fruit. 
As a rule only a small percentage of the flowers of most deciduous fruits 
"set" and many of those that remain fall before the fruit reaches 
maturity. In many fruits there are several distinct periods of dropping, 
these distinct waves being referred to as the first, second and June drops. 
These periods of dropping generally are closely associated with definite 
stages in the development of the tissues of the ovule. Fruit setting, 
fruitfulness and fertility are distinguished. The factors responsible for 
unfruitfulness may be classified for convenience into those which are 
external and those which are internal to the plant. 



CHAPTER XXVII 
UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 

Stout 120 recognizes three types of sterility that are to be attributed 
mainly to internal factors: (1) sterility from impotence, (2) sterility from 
incompatibility, (3) sterility from embryo abortion. Sterility from impo- 
tence arises when one or both of the sex organs fails to develop. This may 
be complete, in which case either no flowers or no sex organs are formed, or 
it may be partial, in which case either stamens or pistils are abortive. 
Sterility from incompatibility arises when, though the sex organs are 
completely formed, they fail to function properly. In the last type of 
sterility the gametes are formed and apparently function but abortion 
of the developing embryo takes place before maturity is reached. The 
same classification may hold for the internally controlled factors with 
which unfruitfulness and the failure to set fruit are associated. It may 
be observed that the sterility due to impotence represents an evolutionary 
tendency in the group or species— an evolutionary tendency that finds 
immediate expression in a distribution of the two sexes between different 
flowers or branches on the same plant or between different plants. The 
distinction between sterility due to incompatibility and that due to 
embryo abortion is drawn in recognition of the time or stage of develop- 
ment at which the male and female gametes, both structurally and func- 
tionally perfect, show their incompatibility — their inability to unite or 
develop together to form a mature embryo. 

Perhaps a classification of the causes of sterility associated with 
internal factors and based upon more fundamental processes would recog- 
nize: (1) those due to evolutionary tendencies, mentioned above; (2) 
those due to genetic influences, regardless of the exact time or stage of 
development when the two kinds of gametes show their mutual aversion 
and (3) those due to physiological factors, in which case there is not true 
incompatibility but a failure of the plant to provide nutritive conditions 
suitable for continued growth. This last type of sterility cannot always 
be differentiated clearly from that due to environmental factors. 

DUE PRINCIPALLY TO EVOLUTIONARY TENDENCIES 

In nature the advantage of cross fertilization in maintaining the vigor 
of the species has resulted in many cases in the development of certain 
characteristics which make self fertilization difficult, if not impossible. 
These factors, so favorable to the maintenance of the species, may, in 

489 



490 FUNDAMENTALS OF FRUIT PRODUCTION 

cultivation, limit its usefulness and range. The more important of 
these characteristics, as they concern the fruit grower, are mentioned 
here. 

Imperfect Flowers : Dioecious and Monoecious Plants. — Most 
fruit-producing species bear perfect flowers. There are some, however, 
in which the sexes are separated. In certain species, such as the walnut 
and pecan, they are found in different flowers on the same tree or plant ; 
in others, such as the papaya and sometimes the strawberry, they are 
found on different plants. 

Monoecious plants bear the pistillate and staminate flowers on the 
same individual and are always fruitful — at least theoretically — and rather 
frequently they are self fruitful. Certainly the segregation of the sexes 
to separate flowers of the plant does not in itself interfere with pollination, 
fruit setting and fruitfulness. Among the more common fruits that are 
monoecious are the walnut, pecan, filbert and chestnut. The members of 
the Cucurbitacese also are for most part monoecious. 

Probably the strawberry is the most widely grown of the dioecious 
fruits. A comparatively large percentage of its varieties bear perfect 
flowers, but some of the best are pistillate. For many years after 
the strawberry was introduced into cultivation no attention was paid to 
the matter of planting so as to secure pollination of the pistillate varieties, 
hence much of the failure of the fruit to set properly in the plantations of 
a century ago. It was not until the observations of Nicholas Longworth 
of Cincinnati were brought to the attention of horticulturists generally 
in the fifties that the unisexuality shown by plants of this species attained 
recognition and planting practices were modified accordingly. Experi- 
ence has taught long since that these pistillate sorts should be interplanted 
with perfect flowering varieties. There are many strawberry varieties 
classified as perfect flowering that produce only small amounts of pollen. 
These, as well as the imperfect sorts, should be interplanted with good 
pollen producers. 

The Japanese persimmon or kaki presents a very interesting case of 
sex distribution. Many of its varieties, such as Tanenashi, Hyakume, 
Hachiya and Costata, produce only pistillate flowers year after year. 
These are called "pistillate constants" by Hume. 70 Certain other varie- 
ties bear each year pistillate flowers and also some staminate flowers; 
these he designates as "staminate constants." Still other varieties bear 
only pistillate flowers some seasons and in other seasons both pistillate 
and staminate. These are called "staminate sporadics." Hume 71 also 
records the occasional appearance of perfect flowers on trees that regularly 
or occasionally bear staminate flowers, though they have not been 
found on plants of the pistillate constant type. In other words, certain 
varieties are monoecious, others dioecious; still others vary from the one 
condition to the other and occasionally a variety becomes temporarily 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 491 

perfect flowering. The study of these flowering characteristics of the 
persimmon and the classification of the more important of its varieties 
has clone much to explain the rather erratic behavior of this plant in 
fruit setting and the maturing of seed-bearing or seedless fruits. 

Even more variable is the distribution of the sexes between different flowers 
and different plants in the papaya. Higgins and Holt 66 recognize 13 classes of 
trees, depending on the combination or separation of stamens and pistils and on 
form of the flower clusters, corolla and fruit. Independent of the classes based 
on features other than sex distribution, these types are: 

1. Pure pistillate flowering plants. 

2. Pure staminate flowering plants. 

3. Plants producing both staminate and perfect flowers. 

4. Plants producing both staminate and perfect flowers, but with sterile 
pollen. These might be called pseudo-hermaphrodite plants. 

5. Plants producing staminate and perfect flowers in which neither pistils 
nor pollen are fertile. The plants might be called sterile hermaphrodites. 

6. Plants producing staminate, pistillate and perfect flowers. 

7. Plants producing pistillate and perfect flowers. 

8. Plants producing staminate and pistillate flowers. 

Types 2 and 5 are necessarily unfruitful, though type 5 is unfruitful appar- 
ently because of incompatibility rather than impotence, for the sex organs are 
developed but non-functioning. Types 1 and 4 are self unfruitful, though it is 
possible that 4 is self barren because of incompatibility rather than impotence. 
The other types are self fruitful; at least fruitfulness is not impossible because 
of impotence. Some of these self fruitful types are dioecious, some are poly- 
gamo-dicecious. Types 1 and 2 are by far the most common; that is, the papaya 
is for the most part unisexual. Consequently in the average planting of that 
fruit it is customary to retain a few of the staminate trees in order to insure a 
good set of fruit on those bearing pistillate flowers. Of course staminate trees 
remain barren, but if there should be only relatively few of them, they probably 
would be valued more highly than an equal number of the fruit producers. 

The fig shows a distribution of its sexes somewhat less complicated than 
the papaya; nevertheless this distribution should often be given careful 
attention at the time of planting. Two kinds of flower clusters are borne 
by fig trees. Certain bear pistillate flowers only. The standard fig 
varieties include trees of this type exclusively. Certain other trees, 
called "capriflgs, " produce both pistillate and staminate flowers within 
the same cluster. As a rule, the staminate flowers are borne near the 
"eye" of the fig and the pistillate flowers near its base. Fig trees may 
thus be placed in two classes in respect to sex distribution, dioecious or 
unisexual trees and monoecious trees. The pistillate flowering trees 
alone produce the figs of commerce. The monoecious trees or caprifigs 
are planted only for the purpose of furnishing pollen for the pistillate sorts. 

Some authorities would take exception to certain of the statements just made 
about the nature of fig flowers. Eisen 40 states that there are three kinds of 



492 FUNDAMENTALS OF FRUIT PRODUCTION 

flowers on trees of the caprifig class — pistillate, staminate and gall. The gall 
flower is regarded as a specialized pistillate that can harbor the pollen-carrying 
Blastophaga wasp but cannot develop seed. Rixford, 112 on the other hand, holds 
that all so-called gall flowers are in reality simple pistillates, not structurally 
different from other pistillate caprifig flowers that occasionally are pollenized, 
set fruit and form seed. Usually they do not have the opportunity to set 
and develop seed because they are not pollinated or because they are stung by 
the Blastophaga and subsequently become galls. 

Eisen 40 and many others recognize a third kind of pistillate flower which 
they call "mule" flowers. These are produced by most of those cultivated 
varieties which yield seedless fruits. They are held to be somewhat different 
in structure from the pistillates of such varieties as the Smyrna, that are capable 
of setting seed. However, Rixford 112 has shown that these so-called mule 
flowers do set and mature seed when properly pollinated and consequently 
considers them true pistillates. 

Heterostyly. — It has been stated that the flowers of many species present 
peculiarities of form and structure, the main function of which is to aid in bringing 
together the male and female gametes so that fertilization may take place and 
reproduction be insured. However, many of these peculiarities of form and 
structure are of such a nature as to prevent self pollination and make cross 
pollination more certain. If cross pollination does not occur, the plant is very 
likely to remain unfruitful even though perfect sex organs have been developed. 

One of these diversities of form is heterostyly, a type of dimorphism in which 
some of the flowers have short styles and long filaments and other flowers of the 
same species or variety have long styles and short filaments. The structure 
and arrangement is such that when these flowers are visited by pollen-carrying 
insects no self pollination takes place but pollen from short stamens is deposited 
upon the stigmas of the short pistils and pollen from the long stamens is carried 
to the stigmas of the long pistils. Cross pollination between two flowers of the 
same form on a single plant may occur, but the arrangement assures a consider- 
able amount of crossing between plants. It has been shown that when the pistils 
of heterostyled plants are pollenized with pollen from the same flowers or from 
other flowers containing stamens of an equal height the union may be fruitful 
but is likely to be attended by varying degrees of sterility. 24 This, however, 
introduces the factor of incompatibility, about which more is said later. 
Apparently heterostyly is relatively unimportant in determining setting in 
deciduous fruits. 

Dichogamy : Protandry and Protogyny. — It has just been pointed out 
that in heterostyled plants the sexes are nearly as completely separated 
and self pollination as completely prevented as in monoecious plants. 
Likewise there may be more or less separation of the sexes and a pre- 
vention of self pollination in perfect flowered plants through the maturing 
of the two sex elements at different times. This behavior of the plant 
is known as dichogamy. If the stamens ripen before the pistil is ready 
to receive pollen the flower is protogynous; if the reverse condition 
holds it is protandrous. Dichogamy is incomplete when there is an 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 493 

overlapping in the seasons of maturity of the two sex elements; otherwise 
it is complete. Complete dichogamy insures pollination with some other 
flower and perhaps with another plant. Incomplete dichogamy tends 
in that direction, but still allows opportunity for a certain amount of 
selfing. 

The frequent occurrence of dichogamy and consequently its impor- 
tance in influencing the setting of fruit is not generally appreciated. 
Kerner and Oliver 78 state: " . . . It appears that all species of plants 
whose hermaphrodite flowers are adapted to cross-fertilization by the 
relative position of anthers and stigmas are, moreover, dichogamous, 
although this dichogamy may be of slight duration. Plants with hetero- 
styled flowers are also dichogamous, since those with short-styled and 
those with long-styled flowers develop at different times. ... As far as 
we can tell at present all monoecious plants are protogynous. . . . 
Alders and Birches, Walnuts, and Planes, Elms and Oaks, Hazels and 
Beeches are all markedly protogynous. In most of these plants . . . the 
dust-like pollen is not shed from the anthers until the stigmas on the 
same plant have been matured 2 to 3 days. Sometimes the interval 
between the ripening of the sexes is still greater. The majority of 
dioecious plants are also protogynous." Both Waugh 134 and Dorsey 37 ' 
call attention to the existence of dichogamy in the plum. Pecan varieties 
have been classified in two main groups, those exhibiting dichogamy and 
those which mature their stamens and pistils simultaneously. 124 

Interesting as illustrating the influence of dichogamy on fruit setting are 
certain experiments of Wester 140 with Anonas. Flowers of the cherimoya 
(Anona cherimolia) and of the custard apple (A. reticulata) were found to shed 
their pollen in the afternoon from about 3 : 30 to 6 : 00. Flowers of the sugar 
apple (A. squamosa) discharge their pollen from sunrise to about 9:00 a. m. 
A few trees of this latter species were found to shed their pollen in the afternoon 
and these same trees did not shed any pollen in the morning. Many pollina- 
tions were made, the results of all pointing to the same general conclusion. The 
following account of one of his experiments illustrates the results obtained: 
" . . . 143 flowers on one sugar apple tree were, in April and May, 1908, pol- 
linated with their own pollen or that of flowers of other plants of the same 
species, 41 with pollen of the cherimoya, 31 with pollen of the pond apple, and, 
51 flowers with pollen of the custard apple. In no instance did fruit set where 
the pollen was applied to the stigma simultaneously with the discharge of its 
pollen; practically all responded where it was applied 15 to 48 hours previous to 
this act, though here, as in the case of the cherimoya, the tree shed much of the 
fruit before it matured owing to its inability to carry it all." 

The flower clusters of the caprifig, the dioecious form of the fig tree, afford 
an extreme and very interesting instance of dichogamy. 40 The stamens and 
their pollen do not mature until shortly before the ripening of the fig, when the 
wasps have attained their maturity in the gall flowers of the same flower clusters 
and are ready to emerge and enter other fruits to which they carry pollen. On 



494 FUNDAMENTALS OF FRUIT PRODUCTION 

the other hand the pistillate flowers of the fig are receptive weeks, or even months, 
earlier. In this way the wasps, carrying the pollen from one crop {e.g., the pro- 
fichi) of the fig, enter the flowers of the following crop (mammoni) at a time when 
their stigmas are receptive. It is possible for self pollination to take place within 
the tree, but there is at least a crossing between two successive crops of the 
caprifig and there is often actual cross pollination between trees or varieties. 

Commenting on the significance of dichogamy Kerner and Oliver 79 remark: 
'' From these facts we may infer that every dichogamous plant has an opportunity 
for illegitimate crossing or hybridization at the beginning or end of its flowering, 
and that dichogamy — especially incomplete dichogamy — is the most important 
factor in its production. Of course this does not exclude dichogamy from playing 
an important part in legitimate crossing as well. On the whole, however, we 
can maintain the view that the separation of the sexes by the maturation of the 
sexual organs at different times leads to hybridization, while their separation 
in space promotes legitimate crossing. The fact that the separation of the sexes 
in time and space usually occur in conjunction harmonizes with this conclusion, 
i.e., that the dioecious, monoecious, and pseudo-hermaphrodite flowers, as well 
as those hermaphrodite flowers whose sexual organs are separated by some little 
distance, are in addition incompletely dichogamous, because by this contrivance 
the flowers of any species obtain (1) the possibility of hybridization at the begin- 
ning or end of their flowering period, and (2) of legitimate crossing during the 
rest of that time. This also explains why incomplete dichogamy is so much more 
frequent than complete dichogamy ; why there are no dioecious species of plants 
with completely dichogamous flowers; and why, if one ever should occur, it 
would of necessity soon disappear. Let us suppose that somewhere or other 
there grows a species of Willow with completely protogynous dioecious flowers, 
that is to say, a species in which the female flowers mature first, and have ceased 
to be receptive before the male flowers in the same region discharge their pollen. 
Hybridization only could occur in it, and the young Willow plants resulting from 
it would all be hybrids whose form would no longer agree absolutely with that 
of the pistilliferous plant. The species would therefore not be able to reproduce 
its own kind by its seed, and it would leave no descendants of similar form; in 
other words, it would die out." 

Data are not available as to the exact degree of dichogamy char- 
acteristic of different species and varieties of the deciduous fruits ; therefore 
it is impossible to state accurately the extent to which it interferes with 
their self pollination or to what extent it is a factor in determining their 
fruit setting. Furthermore, as is shown later, the completeness of 
dichogamy varies considerably with environmental conditions. There 
can be no question, however, but that in many varieties it explains the 
failure of numerous blossoms to set. 

Impotence from Degenerating or Aborted Pistils or Ovules. — It is 
obvious that, if the setting and maturing of fruit usually depend on the 
union of two properly formed sex cells, anything which occurs to interfere 
with the development and proper functioning of either gamete probably 
will result in unfruitfulness or at least in sterility. This occurs in the 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 495 

developing pistils and stamens of many species and is responsible for 
many failures in fruit setting. 

Sometimes degeneration takes the form of an abortion of the entire 
pistil. This may occur early or comparatively late in the course of its 
development; consequently in certain species there are pistils in all 
stages from those very rudimentary and plainly not functioning to those 
that apparently are perfect in structure and ready for fertilization. 
Goff 51 records this condition as very common in many varieties of our 
native plums, and Hodgson 67 states that the same thing is found in the 
pomegranate. It occurs more frequently in the ornamental types of the 
pomegranate than in those varieties cultivated primarily for their fruit; 
in either case it is one of the main causes of the failure of the fruit to set. 
Waugh, 134 in a rather extended study of the occurrence of defective 
pistils in plums, found striking differences in various groups. His 
findings are summarized in Table 1. 

Table 1. — Percentage op Defective Pistils in Different Groups of Plums 

(After Waugh 134 ) 

Domestica group. , t 4.3 Wayland group 10.5 

Japanese group 11.2 Wildgoose group 19 . 8 

Americana group 21 . 2 Chicasaw group 10. 5 

Nigra group 17.0 Hybrids group 18.1 

Miner group 1.9 

In a number of species and varieties the pistils attain their usual size 
and they contain ovules that to the unaided eye appear entirely normal. 
However, examination shows partial or complete degeneration in the 
embryo sac just prior to its maturing; therefore fertilization is impossible. 
Embryo sacs of the orange showing degeneration at various stages in 
their development are pictured in Figs. 2 to 4 of Plate III. Sometimes 
these degenerative processes set in early in the development of the ovules 
and their abortion is so complete that it is evident to the unaided eye 
at the time for fertilization. In the Unshu and Washington Navel 
oranges, however, the fruits may develop in spite of that defect, though 
they are seedless. Embryo sac abortion thus becomes in certain instances 
a cause of seedlessness rather than unfruitfulness. Pistil abortion, 
apparently at a comparatively late stage in development, has been found 
to explain the failure of many strawberry blossoms to set fruit and the 
production of "nubbins" from many others. 131 One of the two ovules 
in the ovary of the plum 37 and other stone fruits is often much smaller 
than the other at the time of flowering, showing that at least a part of the 
almost universal failure of one of the ovules to develop into a seed is 
due to processes operating before the time of fertilization. It should be 
noted in this case, as in many other fruits, that the abortion of a part 
of the ovules of the flower does not lead necessarily to unfruitfulness. 



496 FUNDAMENTALS OF FRUIT PRODUCTION 

The relation of number or proportion of seeds to the holding of the fruit 
is discussed in another connection. 

Impotence of Pollen. — It has long been known that many apparently- 
perfect flowered plants produce only small amounts of pollen and that 
occasionally a considerable portion of that which is borne is non-viable. 
In fact it is unusual to find pollen that is 100 per cent viable. However, 
few data have been available as to the proportion of the pollen produced 
by ordinary fruits under varying conditions that is defective and until 
recently there has been little realization of the importance of this factor 
in determining fruit setting and fruitfulness. 

Beach, 2 > 3 > 4 was one of the first to investigate this subject carefully 
as it pertains to deciduous fruits. He found that varieties of American 
grapes fall readily into three classes in respect to fruitfulness when de- 
pendent on their own pollen for fertilization. These he called self 
fertile, self sterile and partly self sterile. The varieties of the partly 
self sterile group varied from vineyard to vineyard and from season to 
season in their degree of self sterility, but those of the self fertile group 
remained completely self fertile; likewise those of the self sterile group 
remained completely self sterile. Controlled cross pollination experi- 
ments led to the conclusion that the partial or complete self sterility of 
those two groups was not due to any defect in the pistils but to impotence 
in their pollen, though an abundance of it was formed. The stamens of 
the self fertile varieties were erect, while those of the self sterile sorts were 
reflexed. A detailed study of the pollen of these different classes showed 
marked differences in the shape and appearance of the grains. 9 Those 
of the self fertile varieties were oblong, blunt at the ends and quite sym- 
metrical and they germinated well ; those of self sterile sorts were irregular 
in shape and did not germinate well. Stamens of the partly self sterile 
varieties were found to contain some good and some poor pollen. 

A little later Reimer and Detjen 110 reported that all the varieties of 
the Muscadine grape bear reflexed stamens only and that all their pollen 
is defective. Their flowers are pseudo-hermaphrodites rather than true 
hermaphrodites. For fruit to set the pistils must receive pollen from 
male or staminate vines. The plants of this species are essentially dioe- 
cious. Failure to recognize this fact has been responsible for much of 
the unfruitfulness previously encountered in the culture of this group of 
grapes. Among the plants growing wild about three-fourths are stami- 
nate and one-fourth pseudo-hermaphroditic with functional pistils. 74 
More recently there have been found 33 > 73 several plants of this species 
producing true hermaphrodite flowers; these have afforded a starting 
point for the breeding of a new and perfect flowered race of Muscadine 
grapes. 

Apparently the failure properly to set and mature fruit occasionally 
found in European varieties of grapes is likewise due at least partly to 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 497 

defective pollen. 7 This dropping of grape blossoms or of the partly 
developed berries in those of the Vinifera varieties is commonly known 
as "coulure." 

Dorsey 36 has made a study of the cytological changes within the 
developing pollen grain of the grape leading to, or associated with, 
its impotence. Figures 9 to 11 in Plate II show something of the nature 
of these degenerative changes. He distinguishes between what he terms 
sterile pollen and aborted pollen. In the former after true pollen grains 
are formed degeneration occurs in either their generative or vegetative 
nuclei or in both. Aborted pollen results from a development arrested 
at an earlier stage. The following quotation from his report brings out 
the more important details of his investigations: 

"In the formation of the sterile and fertile pollen of the grape the hetero- 
typic and homotypic divisions and the divisions of the microspore nucleus take 
place normally. Sterile pollen in the grape results from degeneration processes 
in the generative nucleus or arrested development previous to mitosis in the 
microspore nucleus. Where degeneration begins early after the division of the 
microspore nucleus, both the generative and vegetative nucleus may be affected. 
If the generative cell is well organized before disintegration begins the vegetative 
nucleus may remain normal. . . . 

"Aborted microspores occur in various percentages in the native forms, as 
well as in the cultivated varieties. While in the end the result is the same, a 
distinction should be made between aborted and sterile pollen. The former occurs 
in both sterile and fertile forms and seems to be due to arrested development soon 
after being liberated from the tetrad, while the latter results from disintegration 
processes subsequent to mitosis in the microspore nucleus, and occurs associated 
with the reflex type of stamen and the absence of the germ pore. . . . 

"The amount of aborted pollen which occurs in the grape varies much in 
different vines. In the 52 cultivated varieties the average per cent, of aborted 
pollen is 22.83, compared with 4.08 in 121 wild staminate vines of V. vulpina 
and 3.70 in 50 wild pistillate. ... Of the 52 cultivated varieties only 10 
have less than 5 per cent, of aborted pollen. . . . 

"The difference between the percentage of aborted pollen in known hybrids 
and the pure forms, among the cultivated varieties, is only slight. The average 
percent of aborted pollen from 10 vines, of varieties generally regarded to be 
pure V. labrusca, is 23.10, while that for 38 of the hybrid varieties is 24.60. 
There are some instances, however, among the hybrids, as in Black Eagle, where 
the amount of aborted pollen is small. . . . 

"Since aborted pollen occurs in much the same relative amounts in the self 
fertile and self sterile varieties, from the standpoint of fertilization and the setting 
of fruit it would seem that the aborted pollen is unimportant in the grape, be- 
cause in the fertile forms there is still an abundance of potent pollen." 36 

It should not be inferred, because the discussion thus far has been 
limited to the grape, that sterility or unfruitfulness due to pollen abortion 
does not occur in other fruits. Pollen abortion is a common occurrence 

32 



498 FUNDAMENTALS OF FRUIT PRODUCTION 

and a frequent cause of unfruitfulness. Osawa 101 reports irregular 
development of the pollen mother cells and much defective pollen in 
Daphne odora. Two to 10 per cent of the pollen of the mango is regu- 
larly defective. 106 Dorsey 37 finds pollen abortion common in the plum, 
noting that in that fruit the disintegration processes usually occur after 
the liberation of the tetrad from the pollen mother cell. If distinction 
is to be made between pollen sterility and pollen abortion, in this case 
as in the grape, the defective pollen of the plum is sterile rather than 
aborted. In neither the plum nor the mango, however, is the percentage 
of defective pollen high enough to interfere seriously with the setting of the 
fruit. Pollen abortion has been reported as a practically constant char- 
acteristic of blackberries in New England. 11 Furthermore it has been 
found to vary greatly with the variety and species. For instance Rubus 
allegheniensis was found to have about 96 per cent, while R. hispidus 
had less than 10 per cent, morphologically perfect pollen. Between these 
extremes were all gradations. The higher percentages of defectiveness 
were enough to reduce very materially the set of fruit. A similar condi- 
tion is reported in the strawberry. 131 

Degeneration occurs in nearly all the pollen mother cells of the 
Washington Navel orange. 18 ' 10 ° Consequently practically no mature 
and perfect pollen grains are formed. In the Unshu variety 100 degen- 
eration is not so general; nevertheless it affects a large number of the 
pollen mother cells. In these two varieties, as in certain others, pollen 
abortion is not accompanied by unfruitfulness because the fruits are 
capable of parthenocarpic development, but it is responsible for partial or 
complete suppression of their seeds. 

DUE PRINCIPALLY TO GENETIC INFLUENCES 
The forms of self sterility and self unfruitfulness discussed up to this 
point are due plainly to factors associated with the fundamental constitu- 
tion of the protoplasm. It is also clear that sterility due to these factors 
is inherited, though the underlying causal agents are evolutionary 
tendencies within the species. Self sterility and self unfruitfulness that 
are to be attributed more directly to genetic factors, to the inheritance 
received, are here discussed under the headings of hybridity and incom- 
patibility. However, it is impossible to differentiate sharply between 
these two types of sterility. 

East and Park 39 remark: "Self-sterility is a condition determined 
by the inheritance received, but can develop to its full perfection only 
under a favorable environment." In his study of fertility in chicory 
Stout 121 found that out of a total of 101 plants in one crop which came 
from three generations of known self sterile ancestry 1 1 were self fertile 
and 90 were self sterile. From his data he was able to conclude not only 
that self sterility is inherited but that in this species narrow breeding 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 499 

is more likely to give rise to self sterile plants than is broad breeding. 
Detjen 32 concluded from his studies with the Southern dewberry (Rubus 
triviaiis) that not only is self sterility in that species transmitted to its 
pure offspring, but frequently to its hybrid progeny. 

Sterility and Unfruitfulness Due to Hybridity. — Unfruitfulness and 
sterility have long been recognized as conditions frequently associated 
with hybridity. Generally the wider the crossing the greater is the degree 
of sterility encountered. Many instances might be cited; a few will 
suffice. Waugh 136 describes a hybrid between the Troth Early peach and 
the Wildgoose plum that has been named the Mule. It bears an abun- 
dance of flowers but they are without pistils or petals. The stamens are 
numerous, but malformed, assuming something of the shape and appear- 
ance of pistils. The variety is fairly constant in its flower characteristics, 
completely sterile and also barren. He mentions another peach-plum 
hybrid, known as the Blackman, with similar characteristics. A hybrid 
between the pear and the quince, described under the name Pyronia, 
flowers and fruits freely but is always seedless. 127 In this case hybridity 
is responsible for sterility alone, instead of sterility and barrenness, as in 
the peach-plum hybrids. The Eoyal and Paradox walnuts, hybrids 
between the Persian and the California and Eastern Black respectively, 
are almost barren. In these cases, as in many other hybrids, barrenness 
due to hybridity is associated with great vegetative vigor. The high 
percentage of aborted pollen found in wild and cultivated blackberries in 
New England is to be attributed mainly to a condition of hybridity. 11 
A number of hybrids between Vitis rotundifolia and various species of the 
Euvitis group have been found almost completely sterile; this is attributed 
mainly to their hybrid condition. 35 In describing one of these V. vinifera 
X V. rotundifolia seedlings Detjen 35 says: 

"Flowers perfect hermaphroditic and imperfect hermaphroditic; stamens 
upright and pistils medium large in the perfect hermaphroditic ; stamens reflexed 
and pistils well developed in the imperfect hermaphroditic flowers. . . . The 
pollen in the perfect hermaphroditic flowers is a mixture of shriveled and plump, 
sterile and fertile grains. The fertility of these plump grains has been demon- 
strated in actual hand-made cross pollinations, also by selling some of the flowers. 
The pollen in the imperfect hermaphroditic flowers is all shriveled and impotent. 
The pistils in both types of flowers are mostly sterile, only two from 17 perfect 
hermaphroditic flower-clusters having developed into berries in 1918. The 
perfect hermaphroditic flowers are sterile because of hybridization, while the 
imperfect hermaphroditic flowers are sterile due to the double phenomenon of 
hybridization and intersexualism with attendant impotence." 

However, abortion of pollen and of pistils cannot always or entirely 
be attributed to hybridity; and, conversely, hybridity is not always a 
cause of unfruitfulness or even of sterility. Many of the cultivated 
American varieties of the grape that are probably pure species bear some 



500 FUNDAMENTALS OF FRUIT PRODUCTION 

aborted pollen and, furthermore, many varieties of known hybrid origin 
are highly self fertile. In discussing this matter Dorsey 36 says: "Since 
both fertile and sterile hybrids occur among the cultivated varieties of 
American grapes, hybridity is not necessarily a cause of sterility. The 
relation of the sterile pollen to the absence of the germ pore, the reflexed 
type of stamen, and the tendency toward diceciousness, suggest that 
pollen sterility in the grape is only a step toward functional dicliny." 
The same investigator 37 reports somewhat more aborted pollen in some 
of the hybrid plum varieties than in some of those of pure species and also 
a tendency for the degeneration processes to start earlier in the hybrids. 

All the available evidence warrants the conclusion that the highest 
fertility is correlated with neither the narrowest nor the broadest breeding 
possible. 

Incompatibility. — One of the most common causes of self unfruit- 
fulness and self sterility is incompatibility between the pollen and the 
ovules of the same plant or of the same variety. That is, both the ovules 
and the pollen of the plant are fertile in themselves, but they fail to 
effect conjugation. Muller found self incompatibility in Oncidium flexuo- 
sum and a number of other species of orchids. 25 In some instances not 
only did the pollen fail to impregnate the ovule but its action was injurious 
or poisonous to the stigmas, causing them to turn brown and to decay 
prematurely. At the same time unpollinated stigmas remained fresh. 
Those that were pollinated with pollen from other plants showed no signs 
of injury; fertilization took place and fruit set; the pollen that acted so 
injuriously upon the stigmas of its own flowers functioned perfectly on 
other plants. The same condition has been reported in Lobelia 2b and as 
not uncommon in Cichorium intybus. 120 

The self sterility or self unfruitfulness that has been reported in the 
apple, 88 ? 107 in pears, 47 ? 132 in the sweet cherry, 50 ? 125 in the plum, 89 ? 134 
in dewberries and blackberries 32 and in the almond 129 is probably in large 
part attributable to incompatibility. In practically all of the instances 
cited the varieties set fruit properly when cross pollinated, showing that 
the pistils were perfectly developed and functional. Furthermore the 
pollen from these same varieties proved viable and capable of taking part 
in the fertilization process and in yielding mature fruits and seeds when 
it was applied to other varieties of the same species. Nevertheless, 
barrenness followed self pollination. However, in most cases data 
are lacking to show whether or not pollination was followed by fertiliza- 
tion. It is possible that in many instances fecundation took place and the 
immediate cause of the failure of the fruit to set or mature was embryo 
abortion at a later stage. This has been mentioned as a distinct cause 
of fruit dropping. It is, however, in most cases very closely related to, 
if it is not actually one aspect of, incompatibility. Therefore the self 
sterility and self unfruitfulness of these common fruits may be considered 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 501 

as due to incompatibility, using that term in its broader sense signifying 
that the normal processes of fertilization fail somewhere between the 
production of functional gametes and the fusion of the sex cells. 

Interjruitfulness and Interfertility. — Just as the terms self fruitfulness 
and self fertility refer to the ability of a plant or a variety to mature 
fruits or seed with pollen from its own flowers, so interfruitfulness 
and interfertility indicate the ability of two plants or two varieties to 
mature fruits and seed with each other's pollen. Varieties that are 
self unfruitful because of dicecism, such as for instance pistillate flowered 
strawberries, figs of the Smyrna type and the date palm, have long been 
known to be interbarren as well. Other fruit varieties, such as many 
of the grapes, that are self barren, or partly so, because of impotent 
pollen, have been recognized as interbarren for the same reason. 34 Until 
comparatively recently, however, it has been the rather general belief 
that most fruit varieties are interfertile, or at least interfruitful, even 
though they might be self sterile, provided that they bear good pollen. 
That is, it was assumed that any variety of apple can successfully 
pollenize and fecundate any other apple variety, the only precaution 
necessary in planting being to choose varieties blossoming at approxi- 
mately the same season. Occasional instances of interunfruitfulness 
were encountered in experimental studies 107 but later work with the same 
varieties in the same or in a different place often proved them interfruitful 
and the first results were regarded as due to accident or experimental 
error. However, Whitaker and Milton, which are open pollinated 
seedlings of the Wildgoose plum, have been reported intersterile and 
though both are fertile when pollinated with Sophie, that variety is 
sterile to their pollen. 137 

In 1913, Gardner 50 reported the three leading varieties of the sweet 
cherry grown on the Pacific Coast as intersterile and interunfruitful 
in Oregon and a little later the same condition was reported for two of 
these varieties in California. 128 At the same time all three varieties 
were found to have perfectly good pistils and potent pollen. This is 
clearly an instance of intersterility due to incompatibility. More 
recently several varieties of the almond have been shown to be inter- 
sterile in California. 129 Stout 120 has found cross incompatibility occurring 
sporadically in his pedigree cultures of chicory and it has been recorded 
in tobacco. 39 In summarizing their observations on cross incompati- 
bility in tobacco, East and Parks state: 39 "Cross-sterility in its nature 
identical with self-sterility was found in every population of self-sterile 
plants tested. The percentage of cross-sterility in different populations, 
based in each case on numerous cross matings, varied from 2.4 per cent. 
to 100 per cent. " 

Cross-sterility is much less common than self-sterility but apparently 
is to be expected in all those groups in which self-sterility exists. Data 



502 FUNDAMENTALS OF FRUIT PRODUCTION 

are not available to show to what extent, if at all, the degree of inter- 
unfruitfulness can be modified by environmental conditions and it is 
not possible to tell, without trial, which varieties are and which are not 
interfruitful. 

In Reciprocal Crossings. — In the investigations with tobacco to which 
reference has just been made, there was found a uniformity of behavior 
between reciprocal crossings. 39 That is, if a certain crossing proved 
sterile, its reciprocal was likewise sterile and if one variety proved incom- 
patible with two others, those two were likewise sterile to each other. 
On the other hand, all grades of opposite results in interfertility have 
been obtained in Verbascum phceniceum when reciprocal crossings were 
made. 117 In some instances when one plant was used as the male and 
the other as the female parent there was complete compatibility and 
when the reverse combination was attempted there was complete incom- 
patibility. A similar condition has been reported in chicory. 120 Vitis 
vinifera, V. bourquiniana, V. labrusca and V. cordifolia hybridize freely 
with V. rouiundifolia and V. munsoniana when the latter two are used 
as the pollen parent, but they hybridize much less freely when the re- 
ciprocal crossing is made. 34 

An interesting case of interf ruitf ulness of a reciprocal crossing but of intersteril- 
ity when the crossing was made one way and interfertility when made the other 
appeared in work done at the Georgia Experiment Station. 41 Flowers of the 
upland cotton, Gossypium Barbadense, were crossed with pollen of the okra, 
Hibiscus esadentus. Perfect cotton bolls were produced but the seeds were non- 
viable. The reciprocal crossing resulted in normal appearing okra fruits and in 
viable seeds. Wellington 139 secured seedless tomatoes by using pollen of the 
Jerusalem cherry, Solanum pseudocapsicum, but no fruit was formed when the 
reciprocal crossing was made. 

DUE PRINCIPALLY TO PHYSIOLOGICAL INFLUENCES 

Besides the effects of evolutionary and genetic influences in limiting 
the set of fruit there are a number of others that can be conveniently 
grouped as physiological, though exact demarcation is impossible. 

Unfruitfulness Due to Slow Growth of the Pollen Tube. — Closely 
related to the unfruitfulness and the sterility due to incompatibility is 
that caused by the very slow growth of the pollen tubes in the style. 
Indeed, this may be considered one type of incompatibility, due to 
chemotropic influences. 

Darwin 29 made many crossings between different forms of heterostyled 
dimorphic and trimorphic plants. He found that when pistils were 
pollinated with pollen from stamens of corresponding height there was 
a high degree of fertility; when pollinated from stamens of a different 
height there were varying degrees of sterility. This sterility ranged 
from slight to absolute. Pollen from stamens of a height corresponding 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 503 

to that of the stigma (legitimate pollination) placed on stigmas 24 hours 
after pollination from stamens of another height (illegitimate pollination) 
was found to effect fertilization, the earlier applied pollen still remaining 
ungerminated. Plants raised from the few seeds obtained from illegiti- 
mate pollinations showed many of the characteristics of hybrids between 
species, being few flowered, weak or perhaps profuse flowered and partly 
sterile. Practically the same has been found in the heterostyled flowers 
of buckwheat. 118 In the legitimate pollinations less than 18 hours 
was required for the growth of the pollen tube and the fusion of its 
generative cell with the egg cell of the embryo sac. In the illegitimate 
pollinations more than 72 hours were necessary for the same series of 
events. Discussing the cause of self-sterility in Nicotiana East and Parks 
say: 39 " . . . The immediate difference between a fertile and a sterile 
combination is in the rate of pollen tube growth. If at the height of the 
season a series of self pollinations and a series of cross pollinations are made 
on a single plant and the pistils fixed, sectioned and stained at intervals of 
12 hours, it is found by plotting the average length of the pollen tubes 
in each pistil against time in 12-hour periods that the growth curve of 
selfed pollen tubes is a straight line which reaches less than half the 
distance to the ovary during the life of the flower, while the curve of 
crossed pollen tubes resembles that of an autocatalysis and reaches the 
ovary in less than 96 hours." Similar differences have been found in the 
rate of pollen tube growth in selfed and crossed apples. 84 

Obviously, slow pollen tube growth alone cannot be responsible for 
a failure of the fruit to set, for eventually the tubes would reach the 
ovules. However, flowers do not remain attached to the flower cluster 
or to the stem indefinitely when fertilization does not occur. Unless it 
occurs within a fairly short time, varying with species, variety and 
environmental conditions, abscission takes place at the base of the style, 
ovary, pedicel or peduncle and fruit setting is prevented. 

The failure of the flowers to set fruit through the retarding of pollen 
tube growth by low temperature is discussed in another connection. 

Premature or Delayed Pollination. — Hartley 58 has found that the 
flowers of tobacco are very susceptible to injury from premature pollina- 
tion. When mature pollen grains are applied to immature pistils they 
germinate, penetrate the styles and enter the ovules and if the ovules are 
not ready for fertilization the flowers soon fall. In cases of this kind 
"the separation of the flower from the plant was rapid and complete and 
not accompanied by any previous wilting of the flower, but invariably 
occurred at a joint situated at the base of the peduncle." This is somewhat 
different from the falling of flowers from other causes. Table 2 shows the 
results of one series of pollinations at various stages of pistil maturity. 
Hartley did not find any injurious results from pollinating orange blossoms 
nine days before opening and but little injury from premature pollination 



504 



FUNDAMENTALS OF FRUIT PRODUCTION 



in the tomato. To what extent premature pollination interferes with 
the set of fruit in the orchard is unknown. 

Table 2. — Influence of Premature Pollination on Setting in Tobacco 

(After Hartley™) 



Number flowers 


Time pollinated 


Per cent set 


20 
40 
' 20 
40 
20 
20 


4 
3 
2 
1 

M 

Wb 


days before opening 
days before opening 
days before opening 
day before opening 
day before opening 
en fully receptive 


5 
5 


77 
95 
95 



It is well known that if pollination is long delayed the blossoms fall without 
setting. Kusano, 87 working with orchids belonging to the genus Gastrodia, found 
that when pollination was delayed for 2 to 3 days fertilization took place in an 
almost normal manner. When it was delayed 4 days it was rather ineffective 
and when it was effective the resulting fruit varied in size "according to the 
number of embryogenic seeds." He also made the interesting observation that 
when pollination was delayed 3 to 4 days a comparatively large percentage of 
the seeds formed were polyembryonic, while seeds resulting from earlier pollina- 
tion seldom contained more than one embryo. 

Nutritive Conditions Within the Plant. — There is abundance of 
both circumstantial and experimental evidence to show that the nutri- 
tive conditions within the plant at and just after the time of blossoming 
are important in determining the percentage of the blossoms that will set 
and also the percentage that will finally reach maturity. 

Effect on Pollen Viability. — Sandsten 114 collected pollen from old 
apple trees in a poor state of vigor and at the same time from strong young 
trees of the same varieties in an adjoining orchard. The average percent- 
age germination of the first lot was 39.8 while that of the second lot was 
56.5. The average number of hours required for germination of the pollen 
from the strong trees was 19.8 ; for that from the weak trees, 28.7. Though 
these differences may not be great enough under average conditions to 
account for much failure to set fruit, it is conceivable that they may 
be of real importance under some conditions. Furthermore, it is possible 
that greater differences frequently exist between the pollen of strong and 
weak blossoms of other varieties and of other fruits. 

Effect on Defectiveness of Pistils. — Goff 51 reported the percentage 
of defective pistils borne by trees of the American varieties of plums and 
consequently their fruitfulness to be closely correlated with nutritive 
conditions within the tree. Exhaustion or weakening one season by 
overbearing, drought or poverty of soil was found to induce the production 
of many defective pistils the following spring. He suggested thinning as 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 505 

a preventive. Dorsey 37 has observed the same occurrence in the plum 
group in Minnesota. He mentions two cases in particular: "One 
variety, Wickson, bore two heavy crops of crossed plums in the greenhouse 
and the following year all pistils were aborted. In the second instance, 
Wolf under orchard conditions bore heavily in 1914, and for three con- 
secutive seasons afterward produced less than 1 per cent of normal 
pistils." Hendrickson 65 mentions two French prune trees in California, 
one of which bore a heavy and the other a light crop in 1916. In 1917 the 
conditions of these two trees were reversed. Paralleling these alter- 
nations in crop yields were differences in the actual percentage of blossoms 
setting and maturing fruit. In each case the light crop was due partly 
to a poorer setting of the blossoms through exhaustion from heavy bearing 
the previous season. 

Fruit Setting of Flowers in Different Positions. — Some fruits, like the 
plum and cherry, bear on both shoots and spurs and it is to be 
expected that slightly different nutritive conditions obtain in these diff- 
erent tissues. Dorsey 37 studied fruit setting of the plum in these positions 
and found a distinctly heavier June drop in the shoot-borne fruits. Some 
of his observations are particularly interesting: 

"In the varieties available in this investigation 200 there was a pronounced 
June drop in the plums borne on the terminal wood. In fact, on the older trees 
fruit seldom matured in this position. The dropping of fruit from the terminal 
growths can be partly accounted for on the basis of the competition from a 
thorn or branch which is developed between the lateral fruit buds on the terminal 
twigs the second season. This condition occurs over the entire outer area of the 
tree. . . . Under favorable conditions fruit matures on the terminal shoots, 
but the percentage to set is small considering the mass of bloom, and even the 
small setting noted above is far in excess of the usual condition when there is a full 
crop on the remainder of the tree. It is apparent that in this position competi- 
tion takes place between fruit and branch as well as between different fruits." 37 

Strong and Weak Spurs. — A number of important correlations have 
been reported between fruit setting in the apple and nutritive conditions 
in the spurs or limb upon which the blossoms are borne. 63 As between 
limbs from the same trees, on those with a light bloom 73.8 per cent of 
the spurs set fruit, while on those with a heavy bloom only 14.1 per cent 
set fruit. Of the spurs on vigorous limbs with large leaves 41.6 per cent 
set fruit; 15.7 per cent set on weak limbs with small leaves. Spurs that 
lost all their flowers and fruit at the time of the first drop had the smallest 
average number of flowers (4.45) and those that finally set had the largest 
average (5.74). Furthermore, a slightly higher percentage of the flowers 
borne on spurs with many flowers actually developed into fruits than of 
those borne on spurs with few flowers. Of 2066 spurs making more than 
1 centimeter growth in length in 1915, 791, or 38.3 per cent, set fruit 
in 1916; of 3,171 spurs making less than 1 centimeter of growth in length 



506 



FUNDAMENTALS OF FRUIT PRODUCTION 



in 1915 only 561, or 17.7 per cent, set fruit in 1916. Five hundred 
ninety-five flower-bearing spurs of several varieties that set fruit 
averaged 2.55 grams in weight; 760 flower-bearing non-setting spurs 
of the same varieties averaged only 1.50 grams in weight. Table 3 shows 
still more clearly the influence of weight of spur on its fruitfulness. In 
a series of defoliation experiments Heinicke found that though 50.6 per 
cent of the check spurs set fruit, only 47.6 per cent of those partly defoli- 
ated and 20.2 per cent of those completely defoliated set. 

Table 3. — Weight of Baldwin Apple Spurs Holding Fruits Varying Lengths 

op Time 
(After Heinicke™) 



Time spur held fruit 


Number of spurs 


Average weight 
in grams 


Until first drop 


30 
28 
30 


2 94 


Until June drop 


3 29 


After June drop 


4.27 







Evidence from Ringing Experiments. — Certain plants which under 
ordinary circumstances would not set and develop fruit partheno- 
carpically have been made to do so by ringing or girdling and thus leading 
to the accumulation of an extra store of food materials above the injury. 
Instances of this kind have been recorded in the gooseberry 42 and grape. 4 
That ringing often does not have such an influence on fruit setting is 
indicated by certain experiments with Nicotiana. 139 It is probable how- 
ever that ringing has quite different effects on various plants and broad 
generalizations cannot be made from the available data. 

Evidence from Starvation Experiments. — Kusano 87 produced experi- 
mentally a series of extreme nutritive conditions in an orchid belonging to 
Gastrodia, at the time of fertilization and during the period of develop- 
ment of the fruit by partly or completely separating the ovaries from their 
source of food. Though the results he obtained probably would not 
apply generally to the developing fruits of other species treated similarly, 
they are instructive in pointing out some of the relations existing between 
fruitfulness, sterility and nutritive conditions. The following quotations 
from Kusano's report summarizes his findings: 

"Imperfect or almost no fruit, but normal seed with embryo: where the 
normally fertilized flower is separated from its nutritive connection. 

"Imperfect or almost no fruit, and nearly normal but embryoless seed: 
when the unpollinated flower is parted from its nutritive connection ; the number 
of seeds is exceedingly diminished. 

"Imperfect or almost no fruit and seed, but almost normal embryo: when 
the fertilized flower is subjected to an extremely unfavorable condition of nutri- 



UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 507 

tion. In this case the typical integument is quite suppressed in development 
and the ovular tissue developed previous to the fertilization stage partakes of the 
formation of the imperfect seed-coat. . . . 

"From the above we see that the embryo does not require during its develop- 
ment the accompaniment of the normal development of the ovarial wall and 
the sporophytic ovular tissue and that the seed-coat alone can develop com- 
pletely, independent of the formation of the embryo, or of the normal develop- 
ment of the fruit-wall. But it must be remembered that a nutritive condition 
which renders the development of the fruit-wall unfavorable may bring about a 
small amount of embryoless seed. 

"In the process of f Ratification the embryo is placed in the first rank for 
development; if the nutritive condition is favorable, it accompanies the develop- 
ment of the seed-coat and fruit- wall; if not, only the latter portions are in high 
degree retarded in development. A similar relation may exist between the 
fruit-wall and the embryoless seed; under the condition which induces most 
ovules to develop into embryoless seeds the fruit-wall develops most vigorously; 
under an insufficient supply of nutritive substances the number of the seed- 
forming ovules is diminished, and in this case the fruit-wall is sacrificed for 
development; in the extreme case of an insufficient nutrition both the fruit-wall 
and a larger number of ovules are suppressed in development, thereby supplying 
limited nutritive material to a few ovules, enabling them to form seed. . . . 
The development of the fruit-wall alone under entire suppression of the ovular 
development is found in some instances of the habitual parthenocarpy." 

It may be noted in passing that the influences of the nutritive condi- 
tion of the plant upon fruit setting, fruitfulness and fertility that have 
been pointed out have been in part upon pistil or pollen abortion and thus 
more or less indirect and they have been in part direct in apparently 
affecting the ability of the developing seeds or fruits to complete their 
maturing processes. No direct or indirect influence on compatibility 
has been noted. On the other hand, experimental studies with chicory 
have led to the conclusion that, at least in that species, "self compati- 
bility and self incompatibility operate independently of the purely 
nutritive relations of the embryos to their parent plants." 122 

Summary. — The individual plants of many species and likewise many 
bud-propagated varieties are self unfruitful because their flowers are 
unisexual and flowers of but one sex occur on a single plant. Among 
deciduous fruits often self unfruitful from this cause the kaki or Japanese 
persimmon and the strawberry are the most familiar. Of more general 
occurrence among fruits is dichogamy. Though seldom complete, 
it accounts for the failure of many individual blossoms to set fruit and 
emphasizes the importance of planting with cross pollination in mind, 
even though the varieties in question are partly self fertile. Heterostyly 
is not important in limiting the "set" of deciduous fruits. Impotence 
(partial or complete) resulting from the degeneration of pistils or ovules 
is very common among certain deciduous fruits. Many varieties, 



508 FUNDAMENTALS OF FRUIT PRODUCTION 

particularly of grapes, produce large numbers of impotent pollen grains 
and they have all the appearance of perfect-flowering sorts, though 
in reality they are pseudo-hermaphrodites. If the embryo sacs degen- 
erate and fruit still forms, seedless specimens are produced. The self 
sterility of many varieties is associated with the hybrid condition of 
the plant. Hybrids between rather distantly related forms are likely 
to be self sterile and often self unfruitful as well. On the other hand, 
there is some evidence that very narrowly bred varieties or strains are 
rather inclined to sterility. When sterility is due to hybridity it is 
likely to be associated with pollen or embryo sac degeneration. Incom- 
patibility is another cause of much self unfruitfulness. This is par- 
ticularly important in the apple, pear, plum and cherry. Not only are 
some varieties self unfruitful but incompatibility exists between them and 
certain other varieties. This characteristic has immediate importance 
in the sweet cherry and almond. In some cases failure to set fruit 
properly is due to premature or delayed pollination or to a slow growth of 
the pollen tube. Unfavorable nutritive conditions within the plant are 
responsible for much failure in fruit setting. Trees that have been 
weakened by overbearing or other causes are very likely to produce 
pistils which are defective or pollen that is low in vitality. There is often 
considerable difference between flowers borne in various positions, or 
between those borne on strong and weak limbs, in their abilities to set 
fruit. 



CHAPTER XXVIII 
UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 

Practically every phase of the environment to which the plant is 
subject just before, at and shortly after the time of blossoming has 
some effect on fruit setting. The influence may make itself felt through 
rendering the plant or the variety more or less completely dichogamous, 
through the production of more or less defective pistils, ovules, embryo 
sacs or pollen grains, through affecting compatibility, indirectly through 
aiding or interfering with pollen transfer or in a number of other ways. 

Nutrient Supply. — It is often impossible to distinguish clearly between 
the influence of nutritive conditions within the plant and of conditions 
of nutrient supply without upon fruit setting, fruitfulness and fertility. 
Though the nutrient supply available to the plant probably acts upon 
fruit setting and development largely through first influencing nutritive 
conditions within, there are so many cases in which the association 
between the two is so evident that the intervening effect of the environ- 
ment upon nutritive condition within is overlooked. Furthermore, 
nutritive conditions within the plant are controlled more readily by 
affording or withholding certain nutrients than by most other means. 
It is therefore desirable to give some attention to nutrient supply as it 
influences fruit setting and fruitfulness. 

Darwin 27 states that much manure renders many kinds of plants 
completely sterile. He cites Gartner as authority for the statement that 
sterility from overfeeding is very characteristic in certain families, 
Graminese. Cruciferse and Leguminosse being mentioned specially. In 
India Agave vivipara is said invariably to produce bulbs but no seeds when 
grown in a rich soil, though when it is grown in a poor soil without too 
much moisture the converse condition holds. 28 On the other hand 
extreme poverty of soil often leads to dwarfing and sterility, certain spe- 
cies of clover being mentioned particularly in this connection. 27 Sand- 
sten 113 found that excessive feeding of tomatoes caused abnormal flowers. 
In some instances the stamens almost aborted; in others the pistils were 
greatly thickened and overgrown. There was a general tendency for the 
overfed plants to produce fruits with fewer seeds. Two plants produced 
seedless fruits of normal size. Though these two plants produced many 
flowers they set fruit poorly. The Jonathan apple, which is usually self 
sterile or nearly so on rich land in Victoria (Australia), becomes self 
fruitful when grown on land of low productivity. 44 The Hope grape, 

509 



510 FUNDAMENTALS OF FRUIT PRODUCTION 

which is classified as a perfect flowered variety of the Muscadine group, 
produces true hermaphrodite flowers only when given proper cultivation 
and care. 33 Under neglect "its pistils gradually cease to function and 
the vine assumes the general role of one that is staminate." This is just 
the reverse of the condition found in the Hautbois race of strawberries, 
which is reported as perfect flowered and productive when grown under 
ordinary culture, though in a rich soil the stamens develop poorly and 
produce little good pollen, the result being a poor setting of fruit. 14 

The data presented in Table 69 of the section on Nutrition are 
particularly pertinent. Applications of nitrate of soda to the trees a week 
or 10 days before blossoming increased the set of fruit by as much as 300 
per cent in some instances. Data are not available to show just how the 
fertilizer applications increase fruit setting, though recent investigations 
indicate that a high nitrogen content in the spur itself favors that 
process. 59 The results of these and similar experiments in other parts of 
the country and with other fruits are of far reaching practical importance, 
for they indicate that fruit setting may be much more completely and 
directly under control than has been realized. 

Pruning and Grafting. — Pruning and grafting result in a changed 
environment for at least portions of the plant and in changed nutritive 
conditions within the entire plant or within certain parts. The general 
influence of these practices on vegetative growth and fruitfulness is 
discussed in some detail in the sections on Propagation and on Prun- 
ing. In addition to those indirect influences on fruit production, how- 
ever, they often have a more direct influence on fruit setting. Thus 
Darwin 26 states that plants of Passiflora alata as grown in England are 
generally self sterile. However, at Taymouth Castle one plant of this 
species grafted on an unknown variety became entirely self fertile. 
Pinching the growing tips of the shoots of certain European grape varie- 
ties when they are 18 to 24 inches long and the blossom bunch is well 
formed helps materially in the setting of the fruit. 8 Pruning, along with 
other practices, is reported to be one of the means of keeping the Hope 
grape (one of the Muscadine group) in a true hermaphrodite condition. 33 
If this is neglected the variety tends to sterility through a weakening and 
an abortion of its pistils. The Malta orange grafted on rough lemon or 
"khatti" stock in Baluchistan produces fruits averaging 16 to 17 seeds; 
when grafted on the sweet lime the fruits of the same variety average 
but seven seeds. 13 In this case the trees have remained fruitful, but 
fecundity has been modified. Though data on this question as it pertains 
to deciduous fruits are almost lacking, there is reason to believe that the 
subject is often of real importance in commercial production. 

Locality. — Fruit setting on trees of the same variety is often much 
better in one locality than in another. It might be possible to segre- 
gate the various factors of soil, temperature, humidity, light, etc., 



UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 511 



that constitute what is termed locality and to assign to each its portion of 
the total influence on fruit setting. This, however, is often difficult and 
from the grower's standpoint it is only the environmental complex and 
the plant's response to it that are discernible. Therefore it is suitable 
to make some mention of the influence of locality in fruit setting, without 
attempting a detailed analysis. 

The common lilac is said to bear seeds moderately well in England 
but in parts of Germany its capsules never contain seed. 27 The America 
grape has been found self sterile in the Experiment Station grounds at 
Columbia, Mo., though it has been reported perfectly self fertile farther 
south. 142 Since the immediate cause of self sterility in the American 
varieties of grape is of two general types — pollen abortion and degeneration 
in the generative nucleus — locality may be considered to have an influence 
on pollen development. Acorus calamus, when grown in certain parts 
of Europe, becomes sterile through the degeneration of both pollen grains 
and embryo sacs. 96 The Jonathan apple is often self sterile in Victoria 
(Australia), 44 though in the United States it is almost invariably self 
fertile. As self sterility in the apple is due usually to incompatibility or 

Table 4. — Percentage of Defective Pistils in Burbank Plum 

(After Waugh lii ) 



Source of flowers 


Per cent 
defective 


Source of flowers 


Per cent 
defective 


Denison, Tex 

Santa Rosa, Cal 

Starkville, Miss 

Auburn, Ala 


27 

9 

36 


Phoenix, Ariz 

Manhattan, Kan 

Parry, N.J 


5 

21 




embryo abortion, the conclusion seems warranted that it is in one of 
these ways that the difference between the localities produces this dis- 
tinctive effect on fruitfulness. 

Still another way in which the factors characteristic of locality influ- 
ence fruitfulness is in the production of defective pistils. Waugh 134 
obtained flowers of the Burbank plum from different sources and found 
the percentages of defective pistils to be as shown in Table 4. He found 
all the pistils of Rollingstone defective in flowers obtained from Minnesota 
City, Minn., and none in a lot obtained from Lafayette, Ind. He 
observed also that in some seasons certain plum varieties were protogyn- 
ous in one locality and protandrous in another. 

A case in which self fertility and fruitfulness vary according to locality, 
apparently through some influence on compatibility, was mentioned by 
Darwin. 30 He stated that " Escholtzia is completely self sterile in the 
hot climate of Brazil, but is perfectly fertile there with the pollen of any 



512 FUNDAMENTALS OF FRUIT PRODUCTION 

other individual. The offspring of Brazilian plants became in England 
in a single generation partially self fertile, and still more so in the second 
generation. Conversely, the offspring of English plants, after growing 
for two seasons in Brazil, became in the first generation quite self sterile." 
Season. — Just as it is almost impossible to separate the influence on 
fruit setting of nutritive conditions within the plant from those of nutrient 
supply without, so it is almost impossible to distinguish the influence of 
locality from that of season. Seasonal variations at the same place may 
give rise to practically the same changes in environment as are occasioned 
by differences in localities during a single season. When this is true 
approximately the same responses to the changed conditions would be 
expected. Darwin 25 stated that Kolreuter had several plants of Verbas- 
cum phceniceum that for 2 years flowered freely and, though self sterile, 
were interfertile with other plants, but that later " assumed a strangely 
fluctuating condition, being temporarily sterile on the male or female 
side, or on both sides, and sometimes fertile on both sides; but two of the 
plants were perfectly fertile throughout the summer." Trees of the 
native plum varieties have been found to vary greatly in fertility from 
season to season 53 and a plum variety that is protandrous one season 
may be protogynous the next. 134 

An interesting case of a return of the potato to the fertile condition 
through seasonal influences has been observed in the Greeley district of 
Colorado. 45 The Pearl variety as grown in that section usually pro- 
duces no flowers. During seasons that are unfavorable for the normal 
development of the plant and its tubers, however, flowers are formed on 
the late branches. Though ordinarily the blossom buds of the potato 
fall off, in this case they opened but no pollen was produced. Thus the 
degeneracy from the standpoint of the potato grower is accompanied by 
some added development in the direction of fruitfulness. A "bastard" 
type is described as occurring sometimes in the Greeley fields of this 
variety; in this there is still further degeneration of the tuber-bearing 
habit, but an abundance of potent pollen is produced. 

End-season Fertility. — End-season fertility of normally self sterile 
plants is rather common. Whitten 142 reports that, " during 1897, Ideal, 
a hybrid (grape) variety, proved to be self impotent early in the season 
but self potent later on, the season being favorable to a succession of 
bloom throughout the summer." He states that since the vine had 
little fruit to carry, it made a vigorous growth and bore a succession of 
flowers. The appearance of the self fertile condition late in the season 
was accompanied by an increasing uprightness of the stamens and pre- 
sumably with the formation of good instead of sterile pollen. A gradual 
decrease in the percentage of defective mango pollen has been noted as 
the season advanced. 106 East and Park 39 found end-season fertility 
developing in their self sterile Nicotiana plants. In this case the imme- 



UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 513 

diate cause of the normal self sterility was a slow growth of the pollen 
tubes, presumably a result of chemotropic influences; the appearance 
of the self fertile condition followed an acceleration in pollen growth. 
These investigators remark: "Since we have reason to believe that the 
difference between a sterile and a fertile combination in these plants is the 
ability of the pollen grain through something inherent in its constitution 
to call forth in the tissue of the style in the former and not 
in the latter case a secretion which accelerates pollen-tube growth, it 
follows that in weakened style tissue some change has occurred that renders 
this secretion more easily produced." They report that self sterility can 
be restored in these weakened plants by allowing them to go through a 
period of rest and then forcing them into vigorous growth. Their sugges- 
tion that "truly self fertile plants cannot be forced into self sterility by 
any treatment" obviously holds if self fertility is defined to agree with that 
concept. However, if that is to be the concept of self fertility it may be 
questioned whether any of our cultivated fruits be self fertile. In the 
fruit plantation there are fruit setting, fruitf ulness and fecundity conditions 
which vary with environment. 

Contrasting sharply with the end-season fertility that has just been 
mentioned as sometimes occurring in the grape, mango and tobacco is an 
end-season sterility found by Valleau 131 to be quite common in the 
strawberry. 

A striking example of seasonal influence on fruit setting and fruitful- 
ness occurs in figs of the San Pedro class. 21 In varieties of this group the 
early crop, or brebas, set freely without pollination, developing seedless 
fruits. The later main or summer crop will not set and mature without 
caprification. This, like the strawberry, is particularly interesting both 
because it is an instance of early season rather than late season fruitful- 
ness and because it is a constant characteristic of these varieties. 

Change of Sex with Season. — Related to the influences of season on 
fruit setting, fruitf ulness and fertility, or, more accurately, to be mentioned 
as the immediate explanation of some of those influences, are the occa- 
sional effects of season upon the complete suppression of one or the other 
of the two sex organs, its effect upon their development when normally 
they are undeveloped or non-functional and its effect upon change of 
sex. The sweet gale or bog myrtle (Myrica gale) is a small shrub which 
grows abundantly in the swamps of Europe, Asia and North America. 
It is described by many authorities as strictly dioecious. However, it has 
been found that intersexes or mixed plants of many gradations are present 
everywhere in the peat moors of England. 31 Furthermore, a study of 
individual plants for a series of years showed that changes of sex occurred 
from year to year. Plants entirely female in 1913 were entirely male in 
1914. Plants female in 1913 were mixed in 1914, entirely male or nearly 
all male in 1915 and again female in 1916. There is a record of a hybrid 

J3 



514 FUNDAMENTALS OF FRUIT PRODUCTION 

grape vine (V. riparia X V. labrusca) which fruited only twice during a 
30-year period, "the pistils evidently varying in strength but being gener- 
ally too weak to produce fruit." 9 Though the date palm is usually 
monoecious, still a tree that ordinarily produces pistillate flowers only may 
develop occasionally a cluster of staminate flowers, or perhaps one year 
produce a few hermaphrodite flowers and never do so again. 104 Certain 
varieties of the Japanese persimmon show great variation in the kinds 
of flowers they bear from year to year. 20 ; 70 In some seasons they 
produce pistillate flowers only and in other seasons they produce a num- 
ber of staminate flowers along with the pistillates. "Seedling (per- 
simmon) trees are very unreliable in the production of blossoms, bearing 
male flowers during the first few years, then a small proportion of female 
flowers, while later the appearance of male flowers is sporadic on some 
trees and regular on others." 20 

Age and Vigor of Plant. — Practically inseparable from the influences 
on fruit setting of nutritive conditions within the plant, of nutrient 
supply without, of locality and of season, is that of age and vigor. The 
change from the production of staminate flowers only to that of some 
staminate and some pistillate flowers and later of pistillate flowers only, 
mentioned in a preceding paragraph as common in seedlings of the 
Japanese persimmon, is a case in point. Young vigorous apple trees 
often fail to set fruit under controlled cross pollinations, when older and 
less vigorous trees of the same varieties set freely. 107 Waugh 134 found on 
the average a higher percentage of defective pistils in young and vigorous 
plum trees than in older trees of the same kinds. The Muscat of Alex- 
andria grape is reported to show marked susceptibility to "coulure" or 
dropping for the year or two after starting to bear, but later this trouble 
is much less serious. 7 Young grape vines have been found to produce 
less pollen than mature vines of the same variety. 9 

In the instances cited, age of plant has been the factor apparently 
associated with the degree or percentage of fruit setting. It is probable, 
however, that age is effective through its influence on vigor and the 
internal conditions of nutrition or hybridity with which vigor is asso- 
ciated. It is interesting that Stout found self compatibility in chicory 
entirely independent of differences in vegetative vigor, thus suggesting 
that some of the internal factors controlling fruit setting and fertility are 
not influenced by vigor. As in the cases where fruitfulness is influenced 
by variations in nutritive conditions, nutrient supply, locality and season, 
most of the influence of varying age and vigor seems to be through 
effects on impotence preceding fertilization and embryo abortion at a 
later stage and not on compatibility, using that term in its narrower 
sense. 

Temperature. — The general effect on the setting of fruit of tempera- 
tures slightly below freezing just before, at or shortly after blossoming is 



UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 515 

well known and in the section on Temperature Relations is a some- 
what detailed account of the more important factors in frost occurrence 
and their bearing upon fruit production. However, temperatures well 
above the freezing point often are important in determining the setting 
of fruit. Darwin 28 calls attention to the rather common failure of 
European vegetables to develop fruits and seeds when grown in India and 
attributes this failure to the hot climate of that country. In some of 
these instances the influence of temperature may be more directly upon 
the formation of flower buds and flower parts than upon the processes of 
fruit setting. 

Goff 53 has shown that though pollen of most deciduous fruits, like 
the plum, cherry, apple and pear, germinates freely at temperatures of 
50°F. or above, the process is practically inhibited by temperatures of 
40°F. or lower. In a number of plums the stigma is receptive for a 
period of only 4 to 6 days. The abscission of the style occurs in from 
8 to 12 days after bloom and it is not influenced to any great extent by 
temperature. 38 On the other hand, the period required for the germina- 
tion of the pollen grain and its penetration of the style may depend on 
temperature and may be as short as 4 days and as long as 12. A period 
of cool, but frostless, weather during blossoming, therefore, may prac- 
tically prevent fertilization and thus very materially limit the set of fruit. 
Presumably similar conditions are found in many other fruits, though 
the relative importance of this factor varies greatly with different 
species and varieties. 

In this connection mention should be made of the indirect influence 
of temperature on fruit setting through its effect on the activity of pollen- 
carrying insects. Evidently the temperature at which bees and other 
pollen-carrying insects will work depends on conditions, for 40°F. has 
been given as the lowest temperature at which the honey bee will take 
flight 38 though normally they do not leave the hive until the temperature 
reaches about 60°F., except after a considerable period of confinement. 
Whatever the exact temperature may be, it is evident that should all 
other conditions be favorable a continued period during blossoming well 
above freezing but still too low for much activity of the pollen-carrying 
insects may account for many failures in fruit setting. 

An interesting example of the influence of temperature on fruit setting is 
furnished by the papaya. Though usually a strictly monoecious plant, the 
"male" form sometimes bears fruit in cool climates. In commenting on the 
change of sex here involved Higgins and Holt remark: 66 "This 'fruiting of the 
male papaya' takes place most freely in cool climates outside the tropics or at 
high altitudes. In Hawaii it may be seen that these trees fruit more abund- 
antly on the mountains than near the sea level. Information received by cor- 
respondence with experiment stations and botanic gardens in many parts of the 
world, in reply to direct inquiry, have confirmed this conclusion. In torrid cli- 



516 FUNDAMENTALS OF FRUIT PRODUCTION 

mates the fruiting of the male is rare. It is to be remembered in this connection 
that all the staminate flowers of the male trees possess an undeveloped or an 
abortive pistil. The only change in the cases mentioned consists in the develop- 
ment of this pistil." 

Light. — It is doubtful if variations in light supply are important 
with deciduous fruits. However, it is of some interest that the willow- 
herb (Epilobium angustifolium) develops its flowers normally and sets 
fruit and seed freely in open sunny situations but when shaded its flower 
buds abort and fall off before opening. 81 In fact, this is true of many 
plants. 

Disturbed Water Relations. — In the section on Water Relations 
it is shown that conditions of low atmospheric humidity, high tempera- 
ture, exposure to high winds and a limited supply of soil moisture some- 
times induce in trees moisture deficits that lead to the formation of an 
abscission layer and the dropping of the blossoms or fruits. The water 
loss in developing Washington Navel orange fruits at and shortly after 
midday has been shown to be as much as 30 per cent. 19 Practically the 
same conditions have been found responsible for much of the shedding 
of the developing bolls in cotton. 48 Studies of boll abscission in cotton, 
however, led to the conclusion that the water deficit in the leaves and 
stems was only indirectly the cause of abscission since the water deficit 
produced in the tissues a rise in temperature which was "the stimulus 
which directly leads to abscission." 

The dropping of flowers or partly developed fruits that is due to 
water deficits is partly under control. Irrigation, tillage, the use of 
certain cover crops and windbreaks are among the more important 
means that tend to lessen the difference between absorption and trans- 
piration in times of stress. 

Discussing the shedding of cotton balls because of water deficits Floyd ex- 
plains how a surplus of water may act in the same way. He says : 

"If the general conclusion that the grand march of shedding is due to the 
depletion of moisture in the deeper soil be true, irrigation and better soil manipu- 
lation are indicated as remedies. It has been shown experimentally by Barre, 
in South Carolina, that irrigation has the effect of inhibiting shedding. The 
observations of Balls that the rise of the water table in Egypt due to the Nile 
floods, by asphyxiating the deeper roots and so limiting the water supply, causes 
severe shedding, are quite in harmony with the above findings, since too much 
water may have quite the same effect as too little, and suitable drainage is thereby 
indicated as surely as irrigation." 48 

Not only may a water deficit lead to the dropping of flowers and newly 
set fruits, but it has been shown experimentally that very high atmos- 
pheric humidity tends to cause the abscission of partly developed apples. 63 

Rain at Blossoming. — Rain at blossoming is recognized generally 
as one of the most important factors limiting the set of fruit. 



UNFRUITFULNESS ASSOCIATED\WITH EXTERNAL FACTORS 517 

The following regarding weather conditions at blossoming time in New 
York verifies this statement; 60 "Wet weather almost wholly prevented the 
setting of fruit in New York in the years 1881, 1882, 1883, 1886, 1890, 1892 and 
1901. Rain is mentioned as one of the causes of a poor setting of fruit in the 
years 1888, 1889, 1891, 1893, 1894, 1898, 1905. . . . Rain and the cold 
and wind that usually accompany it at blossoming time cause the loss of more 
fruit than any other climatal agencies. The damage is done in several ways. 
The most obvious injury is the washing of the pollen from the anthers. The 
secretion on the stigmas also is often washed away or becomes so diluted that the 
pollen does not germinate. It is probable that the chill of rainy weather decreases 
the vitality of the pollen and an excess of moisture often causes pollen grains to 
swell and burst." 

Experimental evidence on the damaging influence of rain on fruit 
setting is furnished by an experiment in which a Mount Vernon pear 
tree was sprayed continuously for 219 hours while in bloom. 43 This 
tree set very little fruit while a tree of the same variety standing nearby 
and not subjected to such treatment set a good crop. Similar results 
were obtained with two Duchess grape vines. 

However, plants possess many protective devices which serve to 
reduce injury to their blossoms from rain. Thus in V actinium and 
many other genera the flower is pendent and the essential organs are 
protected by a bell-shaped corolla; in Opuntia and many others the 
petals close over stamens and stigma during damp weather; the male 
racemes of the Juglandacese and Cupuliferse are pendulous and shed 
water almost perfectly when mature and in Vitis anthers that have 
dehisced and shed part of their pollen close and shut out water upon the 
advent of rain. 77 In the investigation just citied, it was found that 
pollen of the Duchess grape when examined under the microscope 
after 11 days of continuous spraying was apparently uninjured. 43 Work 
with the plum has shown conclusively that after pollination the pollen 
is washed from the stigmas only with great difficulty and that stigmas 
will secrete their fluid a second time if rain removes that first secreted. 38 
Rain, however, is usually accompanied by temperatures below those 
characterizing fair weather at the same season. Thus Hedrick in the 
report just cited states that "rainfall came in periods of prolonged cold 
weather in the years 1881, 1882, 1883, 1886, 1888, 1889, 1891, 1892, 1894, 
1898, 1905. Frosts and cold weather accompanied the rains in 1888, 1889, 
1890, 1891, and 1892." In the light of these and many other observa- 
tions and findings as to the distinctly different effects of low temperature 
on rate of pollen tube growth and time of style abscission, it may be 
questioned if rain at blossoming is in itself a very important factor in 
limiting the set of fruit. Other conditions, particularly lower tempera- 
tures, with which rain is generally associated, and interference with the 
work of pollen-carrying insects, are more important. This statement 



518 FUNDAMENTALS OF FRUIT PRODUCTION 

is not made for the purpose of minimizing the importance of "rainy 
weather" at blossoming in reducing the fruit crop. It is desirable, 
however, that there be a correct understanding of the relative importance 
of the different factors that usually constitute "rainy weather" and that 
there be a realization that even a hard rain, if of short duration and not 
accompanied by very low temperatures, is not ordinarily a serious limit- 
ing factor in this connection. 

Wind. — The average fruit grower regards wind as one of the most 
important agents in the transfer of pollen from stamen to stigma. Many 
plants, such as the walnuts, oaks, hickories and hazels, are wind-polli- 
nated and with these a reasonable amount of wind at blossoming is a 
distinct aid in securing a good set of fruit. However, the majority of 
the deciduous fruit crops are insect-pollinated. With these, wind hinders 
rather than helps pollination, since bees and other pollen-carrying insects 
work most effectively in a still atmosphere and in a strong wind they 
refuse to work at all. Abundant evidence on this point may be found 
in orchards with some exposed and some protected situations. Other con- 
ditions equal, there will be a much better set of fruit where the trees are 
protected from the full sweep of the wind and in exposed places there is often 
a much better set on the leeward than on the windward side of the trees. 

In addition to the indirect effect of wind through interfering with 
the work of pollen-carrying insects, it may operate more directly in whip- 
ping about the flowers and causing mechanical inj uries. It may also cause 
the stigmatic fluid to dry prematurely and thus prevent the germination 
of the pollen grains. In some species at least, the action of wind is more 
pronounced early in the usual period of pistil maturity than later. 38 

There are many cases in which the protection afforded the fruit 
plantation at the time of blossoming is of greater importance than any 
other service rendered by a windbreak. 

Fungous and Bacterial Diseases. — The flowers of many species are 
subject to the attacks of various fungous and bacterial diseases and often 
their work at this time is serious enough greatly to reduce the set of 
fruit. Thus fire blight is generally recognized as one of the most impor- 
tant factors in limiting the set of fruit in pears; the apple and the pear 
scab are responsible for the falling of many flowers of those fruits at or 
shortly after blossoming; brown rot attacks the blossoms of practically 
all the stone fruits; black rot works on grape blossoms, causing many 
to drop; the flowers of the mango 106 are attacked frequently by an 
anthracnose; the list might be extended almost indefinitely. Naturally 
the losses occasioned by these fungous and bacterial attacks at the time 
of fruit setting vary greatly with locality, variety and seasonal conditions. 
For instance, there are certain restricted areas where fire blight of the 
pear and apple is not found, though the disease may levy a very heavy 
toll on pear blossoms a hundred miles distant. The Grimes apple is but 



UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 519 

little subject to the scab fungus and ordinarily its setting of fruit will not 
be materially reduced by it, though a Winesap crop in the same orchard 
may be practically ruined by its work upon the blossoms. In California 
brown rot is a serious disease on the blossoms of the apricot only in 
"regions exposed to ocean influences and does not develop except in 
times of unusually moist weather." 69 

Fortunately most of the fungous and bacterial diseases that attack 
the blossoms of fruit trees can be controlled by spraying or other preven- 
tive measures; consequently losses due to these factors are avoidable in 
many cases. 

Spraying Trees When in Bloom. — Though spraying trees with the 
proper materials* may be effective in preventing the attacks of certain 
diseases that otherwise would seriously reduce the set of fruit, it is not 
necessary or desirable to spray during blossoming. Spray applications 
at that time are seldom recommended and are generally regarded as 
undesirable. They may reduce the set of fruit either directly through 
injuring the pollen or stigma or indirectly through interfering with the 
work of bees and other pollen-carrying insects. 

Beach 5 made a number of laboratory cultures of pollen grains in 
media to which varjdng amounts of Bordeaux mixture alone and Bor- 
deaux mixture with an arsenical poison had been added. He found 
that 200 parts of Bordeaux mixture to 10,000 parts of his culture media 
practically prevented the germination of pollen and that much smaller 
amounts had a distinct inhibiting influence. On the other hand in one 
experiment spraying apricots when in bloom with the regular summer 
strength of the lime-sulfur mixture and with a weak Bordeaux mixture 
caused no injury to the flowers and no interference with fruit setting. 69 
This suggests at least that in actual field practice no great injury in 
fruit setting is likely to result from the use of fungicides alone when trees 
are in bloom. 

Apparently the indirect effects on fruit setting of spraying with 
arsenical poisons when trees are in bloom are much more serious. It 
has been shown that a very small amount of arsenic— less than 0.0000005 
gram of arsenious trioxide— is a fatal dose for a bee and most bees die 
within a few hours after being poisoned. 108 Bees work as freely upon 
sprayed as upon adjacent unsprayed trees. Price 108 found that the mor- 
tality of bees in a check cage was only 19 per cent., as compared with 69 
per cent, in a lime-sulfur-arsenate of lead sprayed cage and as compared 
with 49 per cent, in a sulfur-arsenate of lead dusted cage. 

The suggestion is made that if it has been impossible to spray before 
blossoming for the control of fungi which interfere with fruit setting and 
such fungi are known to be present to a serious extent, spraying may con- 
tinue into, or even through, the blossoming season, but a fungicide alone 
should be used at that time. 



520 FUNDAMENTALS OF FRUIT PRODUCTION 

Other Factors that Cause the Dropping of Fruit and Flowers. — Many 
other agencies besides those mentioned may occasionally cause flowers or 
developing fruits to drop prematurely. Among these may be mentioned 
the presence of small amounts of illuminating gas in the atmosphere. 54 

Bushnell 15 has found that fruit setting in certain cucurbitaceous 
plants is characterized by a distinct periodicity. That is, flowers 
opening during a 2- or 3-day period may set freely, those opening 
during the next 2 or 3 days set poorly, then there is another period of 
good setting and so on. 

Summary. — The most important of the direct effects of the environ- 
ment through the plant itself is in influencing nutritive conditions. 
Soil type, water supply, fertilizers, cultivation and pruning are more 
or less important in this connection. Low temperature and rain are the 
two most important of the environmental factors indirectly affecting 
fruit setting through affording or preventing the opportunity for pollina- 
tion, the germination of the pollen grain and fertilization. 

It is evident from the subject matter presented in this and the two 
preceding chapters that the whole subject of fruit setting is complex. 
In the first place it depends on a number of internal factors, many of 
which are entirely beyond any direct or indirect control. Secondly, 
blossoming generally comes at a season when great fluctuations in 
temperature, humidity and the other features of environment are likely. 
It is therefore not surprising that the response of the tree to the combina- 
tion of all these interrelated factors and conditions varies from year 
to year, from orchard to orchard and even from tree to tree. It is 
fortunate indeed for the grower that the most important of the limiting 
factors to fruit setting — both those internal and those external to the 
plant — are within the grower's control by either direct or indirect means. 



CHAPTER XXIX 

FACTORS MORE DIRECTLY CONCERNED IN THE DEVELOP- 
MENT OF THE FRUIT 

The discussion thus far has been limited mainly to a consideration of 
the primary results of fertilization. From the grower's standpoint, how- 
ever, the nature and extent of its indirect effects are often of equal or greater 
importance. 

The immediate or primary result of fertilization is the initiation of the 
series of changes in the mature embryo sac leading to the development 
of the embryo and endosperm. The changes subsequently occurring 
in the ovarian wall and oftentimes in attached tissues result in the setting 
and development of the fruit. These are the indirect or secondary 
effects of fertilization. 

Stimulating Effects of Pollen on Ovarian and Other Tissues. — Before 
fertilization takes place, the pollen often has an important influence on 
the development of ovarian and other tissues connected with the fruit. 
This effect is independent of the process of fertilization and may be exer- 
cised though fertilization never occurs. For example, Wellington 139 
secured fruits of the Seckel pear by applying to its stigmas pollen of the 
Yellow Transparent apple, and Millardet 93 obtained fruits of certain va- 
rieties of the European grape by employing pollen of A mpelopsishederacea. 
Presumably in neither case could fertilization occur, though the pollen 
tubes may have entered the embryo sacs. Triturated pollen applied 
to the stigmas of certain curcurbits has induced a partial development of 
their fruits 90 and fully formed but seedless fruits of certain species 
have been obtained by applying to their stigmas spores of Lycopodium. 49 
In both of these cases fruit development must be attributed to the stimu- 
lating influence of the pollen or spores. Goodspeed 55 reports that emas- 
culated but unpollinated flowers of the Thompson Seedless grape do not 
set fruit; however, emasculated and pollinated flowers set freely, though 
the resulting fruits are seedless because of embryo sac degeneration. 

Some of the most interesting, and perhaps among the most striking, 
cases of response to the stimulus of pollination are found among the 
orchids. 23 In most species of this family the ovule is in a very rudimen- 
tary stage of development at the time of pollination. In some of these 
if pollination is not effected the ovules never reach the stage at which 
fertilization can take place, but immediately after pollination the tissues 
of the ovule proceed to complete their development and finally reach the 

521 



522 FUNDAMENTALS OF FRUIT PRODUCTION 

stage for fertilization. In many cases several weeks between the time of 
pollination and fertilization are required for the ovules to reach maturity. 

Kusano, 87 who studied the influence of pollination in stimulating the develop- 
ment of the ovary and fruit in Gastrodia, found that many fruits would develop 
in this genus when no pollination occurred. These parthenocarpic fruits were 
normal in appearance, though somewhat below the average in size. Seeds were 
formed but they were without embryos and the number of these imperfectly 
formed seeds was usually below that in fruits resulting from ordinary pollination. 
When Gastrodia flowers are pollinated with pollen of Bletia, another orchid, 
fruits likewise developed but they were much larger than the parthenocarpic 
fruits developing without pollination, though they too were without embryo- 
containing seeds and presumably no fertilization had occurred. Fruits of the 
first category, that is, those developing without the stimulus of pollination, were 
classed as instances of vegetative or autonomic parthenocarpy; those of the 
second class were considered instances of stimulative or aitionomic partheno- 
carpy. Commenting upon the results of some of his experiments, Kusano 87 
remarks: "As regards the parthenocarpic development by the foreign pollen 
two points may be worthy of consideration. First, the size of the resulting 
fruit may depend on the intensity of the stimulus. This is evidenced by the 
experiment with the Bletia-pollinium; pollinated the day of bloom, the pollin- 
ium sends out massive tubes, leading the fruit to maximal growth, but the 
delayed pollination brings about a feebler development of the tube, perhaps 
owing to a certain modified condition of the stigma, and consequently smaller 
fruits result. Further, the pollinia of other orchids yield smaller fruits than the 
Bletia-pollinium, in conformity with the feeble development of the pollen-tubes. 
Secondly, it may be most probable that the size of the fruit correlates with the 
duration of the stimulus acted upon. The product of the normal-sized fruit by 
crossing Bletia appears to be due to the longevity of activity of the pollen-tube, 
remaining alive and vigorous far beyond the period of maturation of the fruit, 
and thus exerting the stimulus unceasingly upon the ovules and ovary throughout 
the interval of their complete development. ... As far as observed in 
Gastrodia, we are led to the view that the ovarial development is correlated 
with the embryogenic development of the ovules when the tube of its own 
pollinium is concerned, but when it is induced by the foreign pollen tube, it is 
likely comparable to the gall formation by the action of fungi or insects. So that, 
though the kind of the stimulus is unknown, whether chemical or mechanical, 
we may ascribe the resulting effect to an incessant stimulus of sufficient intensity." 

The Effect of Certain Stimulating Agents on Fruit Setting. — It 
has long been known that the fruits of certain species which seldom or 
never develop parthenocarpically can be made to set occasionally by 
treating the stigmas with certain stimulating agents other than pollen. 
Indeed the use of Lycopodium spores, mentioned in a preceding paragraph, 
may be regarded as a stimulating agent of this character. Hartley 58 
secured a partial set of fruit in tobacco by treating receptive stigmas with 
magnesium sulfate and other chemicals. The seeds of these fruits 
were poorly developed and without embryos. Wellington, 139 working 
with the same species, obtained some fruits, likewise without good seeds, 



THE DEVELOPMENT OF THE FRUIT 



523 



by "singeing young buds with a hot platinum wire, by exposure of young 
plants to chloroform gas, and by cutting away a portion of the pistil and 
pollinating the stub both with and without the accompaniment of a 
germinative fluid." The ovaries of certain orchids can be made to 
develop into fruits by the mechanical irritation of the stigmas. 23 

Closely related to the effects of mechanical irritation and of various 
chemicals on fruit setting are those of the presence or the stings of 
certain insects. Muller-Thurgau 97 stated that the presence of a certain 
gall insect would cause the setting of pear flowers and a brief rapid 
growth of the fruit, though these insect-infested specimens fell before 
reaching maturity. Figure 54 shows a flower cluster of the LeBrun pear 
shortly after petal fall. The outside flowers had been pollinated, had 
set fruit, and were developing normally; of 
the two center specimens one had not been 
pollinated and was about to drop ; the other, 
infested with the gall insect, had not only 
set but was enlarging much more rapidly 
than fruits developing normally. Kraus 86 
reports that not only fruits but embryo- 
containing seeds often develop from the 
flower clusters of self sterile and self barren 
apple varieties when those flower clusters 
are attacked by aphids. The same devel- 
opment has been recorded in the sweet 
cherry. 50 In such instances the resulting 
fruits are generally much dwarfed and mal- 
formed and seldom can the seeds be made 
to germinate; as a rule the fruits contain 
fewer and smaller seeds than normally devel- 
oped specimens of the same varieties. 102 

Some observations of Johnson 75 on this point are very interesting. Several 
species of cacti often retain their fruits long after maturity. They may persist 
for months or in some cases for years. Johnson, examining a large number of 
plants of Opuntia versicolor in April and May, found only about 25 per cent, 
bearing persistent fruits. However, about 9 out of 10 of those plants which did 
bear apparently normal persistent fruits bore also abnormal gall fruits, the 
result of the stings of one of the gall insects. This led Johnson to suggest, 
"that the cause of the persistence of the normal fruits may be the same as the 
cause of the abnormality as well as of the persistence of the far more common 
gall fruits." 

One of the most interesting cases of the influence of the presence 
of insects, independent of their pollen-carrying activities, on fruit 
setting is found in the male fig, or caprifig. 21 ' 40 ' 112 These are not in 
fact male trees; their flower clusters contain both staminate and pistillate 




Fig. 54. — Fruit cluster of the 
LeBrun pear. The central fruit 
has been parasitized. The outer 
two have set and are developing 
normally. The other one is about 
to fall off. In the cross section, 
larvae are shown at g. {After 
MiUler-Thurgau. n ) 



524 FUNDAMENTALS OF FRUIT PRODUCTION 

flowers. Occasionally some of the pistillate flowers of these clusters are 
pollinated and develop seeds, but as a rule if the Blastophaga wasps enter 
the cluster they oviposit in the pistillate flowers and so-called gall flowers 
result. While the larvae of the Blastophaga are developing in the gall 
flowers the staminate blossoms of the cluster mature so that their pollen 
is shed when the mature wasps are ready to emerge. Such flower 
clusters on the caprifig are known as insectiferous figs. If, however, the 
Blastophaga wasps do not enter these clusters at the stage when their 
pistillate flowers are ready for pollination or oviposition, the cluster 
may or may not persist until its staminate flowers mature their pollen. 
(From a practical standpoint their remaining and maturing is of no 
value, since no wasps are in them to emerge and carry pollen to the 
flowers of pistillate trees.) Such clusters are known as polliniferous figs. 
In any case they drop off before the insectiferous figs reach full maturity 
and the dropping is in a way comparable to the June drop of many other 
fruits. Since pollination is unnecessary for the setting and persistence 
of the insectiferous fig it must be concluded that the mechanical or chem- 
ical stimulus resulting from the insect's presence is the real cause of 
setting. The growth stimulus changes the twigs and branches 40 bearing 
insectiferous figs so that they may be told readily from those bearing 
only polliniferous figs by their thickness, length and general vigorous 
appearance. This response, not unlike that frequently attending the 
injection of some chemical substance into vegetative tissue, is at least 
suggestive of the complexities involved in fruit setting. 

Seedlessness and Parthenocarpy. — Seedless fruits are found in 
practically all fruit-producing species. In some cases they are of rather 
infrequent occurrence, their production apparently depending on unusual 
conditions of culture or environment. In others they appear frequently 
and many seedless strains or varieties have been established and are 
propagated extensively by vegetative means. In such cases the seed- 
lessness is due primarily to internal causes that are usually but little 
influenced by changes in environment. 

Investigations with the grape by Stout 123 have led to this conclusion: "The 
most effective course in breeding for the development of seedless sorts is suggested 
by the conditions of intersexualism. Most individuals and varieties producing 
seedless or near-seedless fruits are strongly staminate. The former can be used 
as male parents on the latter, which do produce a few viable seeds. Plants 
strongly male and seedless can be crossed with plants strongly male but weakly 
female and near-seedless and, also, the self -fertilized progeny of the latter may 
be obtained. In this way families weak in femaleness may undoubtedly be 
obtained in which a considerable number of individuals will produce seedless 
fruits." 

Parthenocarpy refers to the ability of a plant to develop its fruit (1) 
without fertilization or even (2) without the stimulus that comes from 



THE DEVELOPMENT OF THE FRUIT 525 

pollination. In other words, the growth of the ovarian and other 
tissues of the fruit can occur without any stimulus from the accom- 
panying development of the ovules into seeds. Parthenocarpic fruits are 
usually, but not always, seedless. In some species fruits will develop 
and viable seeds will be formed even if no pollination takes place. Such 
plants are parthenocarpic and parthenogenetic at the same time. (Par- 
thenogenesis is common in certain strawberry varieties.) Furthermore, 
many parthenocarpic fruits contain aborted or partly developed seeds, 
or seeds that, though normal in appearance, are incapable of germination. 
On the other hand, not all seedless fruits are parthenocarpic. In some 
cases seedlessness is due to embryo abortion some time after fertilization ; 
unless pollen had been available to furnish the stimulus for fruit setting 
no later development of the fruit would have been possible. 

It is evident therefore that seedlessness and parthenocarpy are 
rather distinct phenomena though it frequently happens that the two 
are associated. 

Seedlessness of N on-parthenocarpic Fruits. — The immediate cause 
of seedlessness in fruits that have not developed parthenocarpically is 
embryo abortion. This in turn may be due either to internal or to exter- 
nal factors. Frost or freezing temperature after the fruit has set is 
perhaps one of the most common of the environmental factors leading to 
this condition; it has been observed repeatedly in pears, apples and 
peaches. The developing embryo of the seed seems for some reason 
more tender to low temperatures than the ovarian and other tissues 
surrounding it. Consequently embryo development is arrested; how- 
ever, if the growth of the fruit has proceeded far enough it will continue 
through to maturity, though such fruits are often materially smaller 
than those containing seeds. In many pear varieties, particularly 
those that normally are either elongated or pyriform, the seedless speci- 
mens are generally quite distinct in shape. 12 Each has a shorter trans- 
verse diameter through the core, but is much thickened at the basal end. 
Sandsten 113 has produced seedless tomatoes by excessive feeding. 
Though no statement is made as to whether or not these fruits developed 
parthenocarpically, it is presumable that pollination at least and prob- 
ably fertilization took place and that seedlessness was due to embryo 
abortion. 

In a preceding paragraph it was shown that full maturity of the fruits 
on a caprifig tree is usually attained only when some of its pistillate 
flowers are inhabited by the developing Blastophaga wasp. Ordinarily 
these fruits mature no seeds because few or none of the pistillate flowers 
are pollinated. In this fruit, then, embryo abortion and seedlessness are 
associated with a stimulus resulting from the attack of a certain insect. 

Embryo abortion, resulting in seedlessness, is not, however, always 
due to external factors. For instance, according to one investigator only 



526 FUNDAMENTALS OF FRUIT PRODUCTION 

about 25 per cent, of the fruits of the Blue Damson plums contained good 
plump seeds. 89 The remaining 75 per cent, were seedless or their seeds 
were only half grown and non-viable. Many other plum varieties were 
found to bear a large percentage of seedless fruits. Nevertheless, none 
of these varieties developed fruit parthenocarpically and in some of them 
cross pollination was necessary for any set at all. " The kind of pollen used 
seems to have had little bearing upon the relationship of fruit production 
to seed production, as the percentage of seeds developed in any variety 
seems to be rather constant regardless of the kind of pollen used." 89 
The same type of seedlessness has been observed in many sweet cherry 
varieties, in the May Duke cherry reaching sometimes over 95 per cent, 
of the fruits. Seedlessness that is not associated with parthenocarpy is 
likewise frequent in some of the cultivated varieties of the filbert, where 
it is a serious matter since seeds constitute the crop. A thorough study 
would undoubtedly show that seedlessness is frequently associated 
with embryo abortion in the developing seeds of many cultivated fruits. 
Though in many varieties if seed abortion takes place at any stage 
the fruit drops prematurely, in many others it can occur at a late, and 
still others at an early, stage and still the fruit will persist and mature 
properly. Evidently seedlessness from this cause depends on the 
varying requirements of the ovarian tissues of different fruits for the 
stimulus imparted to them by the growth of the partly developed 
seeds within. Instances of this kind, however, probably always follow 
fertilization. 

Vegetative and Stimulative Parthenocarpy. — Distinction has been 
made between vegetative or autonomic and stimulative or aitionomic 
parthenocarpy. In certain species parthenocarpic development is 
vegetative; in other species it is stimulative; in still others both kinds 
occur. The cases of parthenocarpy that have been reported for a number 
of species have not been studied carefully enough to make possible 
their classification. Among the fruits reported as vegetatively partheno- 
carpic may be mentioned the banana, 1 many varieties of the Japanese 
persimmon, 70 -' 71 certain mulberries, 16 certain peach varieties, 119 the 
medlar, 82 the papaya, 66 the egg plant, summer squash and the English 
cucumber, 98 a number of varieties of the orange 100 and many varieties 
of the fig. 40 These fruits, or certain of their varieties, either occasionally 
or regularly set and mature fruit without the stimulus even of pollination. 
Among those that have been reported parthenocarpic when subjected to 
certain stimuli, usually the stimulus of pollination, are the pepino, 99 
tobacco, 139 pear 139 and Jerusalem cherry. 139 Many varieties of Musca- 
dine 110 and of Labrusca and Labrusca-hybrid grapes 3 have been reported 
as occasionally or sparingly parthenocarpic when subjected to the stimu- 
lus of pollination with impotent pollen, and the Thompson Seedless 55 grape 
is regularly parthenocarpic under similiar conditions. 



THE DEVELOPMENT OF THE FRUIT 



527 



In discussing the influence of nutritive conditions within the plant 
on fruit setting attention has been directed to their influence on 
parthenocarpy. Apparently unusual accumulation of elaborated foods 
in proximity to flowers in the receptive stage often acts as a stimulus to 
further growth and development and in this way inhibits the formation 
of an abscission layer much as would the stimulus occasioned by the 
stings of certain insects or by developing seeds. 

Relation of Anatomical Structure of Fruit to Parthenocarpy. — As 
has been pointed out, seedlessness is to be expected at least occasionally 
in almost every species and variety and it is probable that the same may 
be said of parthenocarpy. It may be noted, however, that it is more 
frequent in species whose fruits the botanist classifies as inferior, those 
into whose structure tissues other than the ovary enter. Though this 
may be a mere coincidence, it at least suggests that the greater stem-like 
character of such fruits imparts to them a stronger tendency to persist 




Fig. 55. — Developing fruits of the LeBrun pear; a and d normal seed-containing 
fruits; b, c, e and / seedless. (After Miiller-Thurgau. 97 ) 

than there is in those whose tissues when mature are entirely carpellary 
in nature. They seem to be less in need of the stimulus of fertilization. 
In Fig. 55 are shown pears of the LeBrun variety, one of which is develop- 
ing as a result of the stimulus afforded by pollination and fertilization. 
The other two are developing parthenocarpically. The greater develop- 
ment of the stem tissues in the latter case is very suggestive. 

Suggestive also in this connection are the following statements by Johnson 75 
on the perennation and proliferation of the fruits of Opuntia fulgida. "It is 
true that the vegetative joints and both the fertile and sterile fruits resemble 
each other greatly in their capacity for proliferation. There seems no adequate 
reason, however, for assuming that either the proliferating habit or the funda- 
mental structure of the fruit is a secondary thing in the evolution of the opuntias. 
On the contrary, it is natural that the thick-skinned, water-stored joints of 
these cacti should have proved capable of persisting on moderately moist soil 
until rooted deeply enough to secure a water-supply adequate for the starting 
of a young plant. The fruit being . . . really a stem in organization, up to 



528 FUNDAMENTALS OF FRUIT PRODUCTION 

the latest phase of its development, it is also very naturally capable of prolifera- 
tion to root and shoot. The capacity of joint and fruit for persistence and pro- 
liferation is probably as old as the fleshy character of the family. The persistence 
of the sterile fruits, at least to maturity, is not a really surprising thing, in view 
of the preponderatingly vegetative and stem-like character of the bulk of the 
wall of the ovary. Sterile ovaries occur in many species of angiosperms, but in 
most of these the carpels constitute the bulk of the fruit. Therefore, when the 
seeds are wanting in these forms, and the carpels as usual fail to develop, no 
fruit is formed and the flower bud soon withers and drops off. In Opuntia, on 
the contrary, even if the seeds and carpellary portion of the fruit do fail to develop, 
the basal stem-like part may go on, practically unhindered in its vegetative 
growth, and mature quite normally." 

Between the conditions represented by autonomic parthenocarpy 
on the one hand and varietal interunfruitfulness on the other there is a 
series exhibiting practically all possible expressions of the tendency to set 
and mature fruit. Only a little less extreme than the tendency to fruit- 
fulness shown by plants vegetatively parthenocarpic is that of plants 
aitionomically parthenocarpic. Next in the series are the plants that 
can set and mature fruit if self pollinated and fertilized, though embryo 
abortion takes place almost at once. These in turn are followed by 
plants which require varying degrees of development in the seeds that 
they may properly mature their fruit. Finally there are those that 
require the maturing of viable seeds along with the developement of their 
fruits else premature dropping will occur. 

The Value of Seedless and Parthenocarpic Fruits. — Seedlessness in 
edible fruits is generally regarded as a valuable variety characteristic 
for commercial purposes. In many cases at least the market is willing to 
pay a premium for it. Mention of the regard in which seedless grapes and 
oranges are held is ample evidence. Bananas and pineapples containing 
seeds would probably find a very limited market. Even a material 
reduction in the number of seeds would be a great asset in the blueberry, 
the blackberry, the watermelon, the sugar apple and in many other 
fruits. On the other hand, in many fruits seedlessness would not be an 
asset. There would be little advantage in seedless apples or pears, if the 
carpels remained. It has been pointed out that many fruits of our 
ordinary plum and cherry varieties are seedless, but this condition is not 
generally known or even suspected because the bony endocarp (stone) 
remains unchanged. 

For the grower, parthenocarpy probably is a more valuable variety 
characteristic than seedlessness. If his fruits are parthenocarpic he is 
insured against crop failure from self and cross unfruitfulness and, if 
their parthenocarpy is autonomic, through failures resulting from lack 
of pollinating agents or pollinating weather, his setting of fruit is more or 
less guaranteed. It should not be inferred, however, that all the flowers 
of parthenocarpic varieties set fruit and that all these fruits mature. 



THE DEVELOPMENT OF THE FRUIT 520 

Mention has been made of the relation of water deficiencies at blossoming 
or shortly thereafter to dropping in the Washington Navel orange. 19 
Many other agencies that limit fruit setting in non-parthenocarpic 
varieties cause the dropping of those varieties that develop partheno- 
carpically. In other words, the parthenocarpic condition is only a partial 
and not a complete insurance against crop failure from premature 
dropping. 

From a practical standpoint seedlessness and parthenocarpy are to be 
considered more as varietal characteristics to be sought when breeding 
or originating new varieties or strains, rather than as conditions to be 
produced by cultural means. 

The Relation of Seed Formation to Fruit Development. — It has just 
been pointed out that in some species or varieties ovarian and other 
tissues of the fruit may develop independently of those of the enclosed 
ovules. This condition, however, is by no means universal and such 
parthenocarpic fruits are usually somewhat different in size, shape or 
other characteristics frcm seed-containing specimens of the same kinds. 
Furthermore, in the seed-containing specimens important differences in 
development are often associated with varying seed ' number and 
distribution. 

Structure of Fruit. — Evidence that certain tissues of the pear undergo 
a proportionally greater development in seedless than in seed-containing 
specimens is presented in Fig. 55. That this is very common in other 
fruits is indicated by the work of many investigators. Thus in seedless 
eggplants the outer portions of the fruit grow more rapidly than the inner 
portions, "the placentae evidently requiring the stimulus of the growing 
ovules to induce development." 98 In seedless fruits of the eggplant and 
in those in which the development of the ovary is arrested at an early 
stage there is sometimes a very marked and abnormal development of 
the subtending calyx. "Usually the most prominent indication that 
impregnation has taken place, in the eggplant, is the rapid growth 
of the calyx. Many times, however, the calyx becomes much enlarged 
while for some reason the ovary fails to develop. I have frequently 
seen examples of this, in which the calyx was fully 6 inches long." 98 
Ewert 42 studied the structure of seedless and seed-bearing gooseberry 
fruits and found striking differences in their cell size and structure. The 
cells of the placentae and inner ovarian wall of seed-containing fruits 
averaged 45-90^/x in diameter, while many of those in the seedless speci- 
mens were seven or eight times as large. 

Form. — The pears shown in Fig. 55 are illustrations of changes in form 
accompanying changes in internal structure due to seedlessness. Mun- 
son 98 observed that the parthenocarpic seedless fruits of English cucum- 
bers were cylindrical in shape, but that when they were pollinated and 
seeds developed the apical one-third of each fruit was much enlarged, 

34 



530 



FUNDAMENTALS OF FRUIT PRODUCTION 



owing to the location of the seeds in that end and not in the basal portion. 
Seedless or nearly seedless specimens of Taber No. 129, a variety of 
Japanese persimmon, are almost conical and distinctly pointed, while 
seed-bearing specimens of the same variety are oblate. Furthermore, 
"Taber No. 23 when seedy is oblate-rounded, but when seedless it 
assumes an almost quadrangular form with very blunt or rounded corners. 
Zengi is oblate-rounded when seedy, but approximates a truncated cone 
in shape, or is distinctly oblong when seedless." 70 

Size. — Perhaps an even more striking influence of seed formation 
on the development of the fruit is in size. Seedless grapes are much 
smaller than seed-containing berries of the same variety and berries 
containing aborted seeds are intermediate between those that are seed- 
containing and those that are seedless. 4 Seed- containing gooseberries 
have been found to average 5 grams in weight, while seedless berries of 
the same variety averaged only 3 grams. 42 Seedless apples and pears 
are often, though not always, smaller than seed-containing specimens. 
In the date palm the seedless fruits maturing from unpollinated flowers 
are only one-third to half the size of normal seed-containing fruits of the 
same varieties; 105 

Furthermore in fruits normally containing a number of seeds consid- 
erable correlation is likely between the size of the fruit and the number of 
seeds developing. Munson 98 found this true in the tomato and he 
observed that the locules were well developed only on the side of the fruit 
containing a considerable number of good seed. The influence of seed 



Table 5. — Number of Seeds in Fruits That Drop and in Fruits That Remain 

(on the Apple Tree) 
(After Heinicke 63 ) 



Number of 


Bale 


win 


Rhode Island 


Maiden Blush 


seeds to 
the fruit 


Attached 
fruit 


Drop 

fruit 


Attached 
fruit 


Drop 

fruit 


Attached 
fruit 


Drop 

fruit 


1 




2 




6 


1 


3 


2 


5 


16 




13 


4 


17 


3 


9 


12 


4 


18 


9 


17 


4 


9 


7 


1 


9 


7 


8 


5 


14 


4 


5 


15 


4 


6 


6 


6 


6 


5 


2 


10 


7 


7 


3 




5 


1 


10 


3 


8 


1 


1 


6 


2 


11 


4 


9 






1 




6 




10 






1 




2 




11 






1 








12 










1 




13 










1 





THE DEVELOPMENT OF THE FRUIT 



531 



number on the premature dropping of apples is shown by data summarized 
in Table 5. Though the possession of a certain number of developing 
seeds did not insure the fruit against dropping and though some of the 
few-seeded fruits persisted and matured, there was a well-marked tend- 
ency for the latter to fall prematurely and an equally distinct tendency 
for the several-seeded fruits to persist. In a previous paragraph it was 
pointed out that the setting and maturing of apples is favored by the size, 
strength and vigor of the limbs and spurs on which they are borne. Table 
6 presents further data which show the varying seed numbers in fruits 
of approximately the same size but borne on spurs of varying weights. 
It is noticeable that with fruit weights remaining constant the number 
of seeds they contain varies inversely as the weights of the spurs. In 
other words, the poorer development of fruit generally found on weak 
spurs is offset if the fruits have enough seeds. This has led to the sugges- 
tion that developing seeds have a pulling power for water and sap, 
enabling the fruits of which they form a part to develop more or less at 
the expense of other fruits with presumably smaller food-attracting 
abilities. 63 



Table 6. — Seed Number Compensating for Spur Weight in the Apple 

(After Heinicke 63 ) 
(Weight of fruit constant, number of seeds and weight of spurs varying) 



Lot 



Variety 



Fruit 
weight 
(grams) 



Number 
of seeds 
per fruit 



Spur 
weight 
(grams) 



Tompkins King 

Tompkins King 
Tompkins King 
Tompkins King 
Rhode Island . . 
Westfield 



54 
05 
31 
98 



3.97 
1.45 
6.09 
3.75 
5.05 
2.40 
4.86 
2.28 
2.33 
1.31 



Experimental evidence in corroboration of. this suggestion was obtained 
by coating with vaseline partly grown apples on spurs removed from trees 
and exposed to a drying atmosphere. It was found that the leaves on the spurs 
were able to withdraw less water from many-seeded than from few-seeded fruits 
and more from the side of a fruit having no seeds than from the side where the 
locules contained a number. 63 



532 



FUNDAMENTALS OF FRUIT PRODUCTION 



Miiller-Thurgau 97 found a similar correlation between fruit size 
and number of seeds in grapes, as is shown in Table 7, and Valleau 131 
found the size of strawberry fruits closely correlated with the number 
of their akenes. 



Table 7. — Relation of Seed Number to Fruit Size in Grapes 
(After Muller-Thurgau 97 ) 





Seedless 


1 seed 


2 seeds 


3 seeds 


4 seeds 


Variety 


Flesh, 
grams 


Flesh, 
grams 


Seeds, 
grams 


Flesh, 
grams 


Seeds, 
grams 


Flesh, 
grams 


Seeds, 
grams 


Flesh, 
grams 


Seeds, 
grams 




25.0 
27.9 
23.7 

58.7 
60.3 


58.2 
52.9 
81.6 
135.8 
112.6 


2.1 
1.8 

2. 14 
2.4 

3. 1 


77.2 

92.4 

116.7 

196.6 

202.0 


3.9 

3.7 

4.12 

5.0 

7.4 


89.0 
110.5 
140.8 
232.7 
244.4 


5.2 
5.2 
5.9 
7.4 
10.9 


112.0 
140.0 
155.8 

258.8 


6.0 


Early Burgundy 

Portugieser 

White Gutedel 


7.3 
6.9 

14.9 











It should not be inferred, however, that seedless fruits are always 
smaller than seed -containing fruits of the same varieties or that fruits 
containing many seeds are larger than those containing but few. For 
instance, in his pollination work with plums, Marshall 89 found that 
many varieties mature a large precentage of seedless fruits. These 
cannot be distinguished from those containing seeds by their size or any 
other external characteristic. The same is true of fruits of the sweet 
cherry. Furthermore it has been found that seed-bearing fruits of the 
Japanese persimmon are uniformly smaller than seedless specimens 
of the same varieties. 70 

Composition and Quality. — Associated usually with differences in 
the structure of fruits are variations in composition and quality. This 
holds true for the structural changes associated with varying seed number, 
and indeed the differences in composition are often greater than would 
be expected from observation of the variations in structure. Table 8 
shows the sugar content and acidity of seedless and normal pears and 
Table 9 shows differences in composition between caprified and un- 
caprified figs of several varieties. The difference in acidity between 
the seedless and seed-containing pears is striking and is sufficient to 
make a considerable variation in quality. Though the distinctions 
between the caprified and the uncaprified figs are on the whole less 
prominent they are great enough to be of commercial importance in 
such varieties as the Dottato. There are differences also in color of 
flesh between caprified and uncaprified figs of the same variety. 112 

Perhaps the most striking dissimilarities in composition and quality 
between seedless and seed-bearing fruits are found in certain varieties 
of the kaki or Japanese persimmon. Zengi, Hyakume and certain other 
sorts are always solid, dark fleshed when they have a good supply of 



THE DEVELOPMENT OF THE FRUIT 



533 



Table 8. — Influence of Seed Number on Sugar Content and Acidity in 

Pears 

{After Ewert A2 ) 



Grams of reducing sugar in 100 
cubic centimeters of sap 



Grams of acid, calculated as malic 

acid, in 1000 cubic centimeters of 

sap 



Fruits seedless. 
Fruits 1-seeded 
Fruits 2-seeded 



5.81 
8.33 
9.26 



0.98 
1.61 
1.79 



Table 9. — Analyses of Caprified and Uncaprified Figs 
{After Condit- 1 ) 



Variety 



Analysis by 



Per cent 
water 



Per cent 
sugar 



Fig d'Or, caprified 

Fig d'Or, uncaprified 

Fig Datte, caprified 

Fig Datte, uncaprified 

Bourjassotte, caprified 

Bourjassotte, uncaprified 

Adriatic, caprified 

Adriatic, uncaprified 

Dottato, caprified (Kadota) 

Dottato, uncaprified (Kadota) . . 

Dottato (dried), caprified 

Dottato (dried), uncaprified 

Adriatic (half dried), caprified 
Adriatic (half dried), uncaprified 

Adriatic (fresh), uncaprified 

Adriatic (fresh), caprified 

Adriatic (dry), uncaprified 

Adriatic (dry), caprified 



Du Sablon 
Du Sablon 
Du Sablon 
Du Sablon 
Du Sablon 
Du Sablon 
W. V. Cruess 
W. V. Cruess 
W. V. Cruess 
W. V. Cruess 
F. W. Albro 
F. W. Albro 
F. E. Twinning 
F. E. Twinning 
M. E. Jaffa 
M. E. Jaffa 
M. E. Jaffa 
M. E. Jaffa 



80.00 
74.00 
71.00 
71.00 
70.00 
76.00 



22.57 
25.75 
27.05 
28.70 
70.70 
74.70 
18.00 
16.00 



11.20 
12.60 
14.30 
18.70 
3.50 
6.20 
19.05 
18.00 
35.20 
28.40 
75.36 
68.16 
34.80 
35.50 
18.78 
13.00 
51.50 
48.50 



seeds, or when there are only three or four seeds and these are well 
distributed. 70 When there is only a single seed, or two or three seeds 
in adjacent locules, the flesh surrounding these is dark while that some 
distance away is light colored. When these varieties produce seedless 
fruits all of their flesh is light colored. O'kame and Yemon, possessing 
full complements of seeds, have dark colored flesh immediately surround- 
ing the seeds, but light colored flesh next to the skin. Tsuru, Costata, 
Triumph and some others are light fleshed whether seeds are present 
or not. The dark flesh of persimmons is edible while still hard and firm, 
but the light flesh remains astringent until it softens. Hume 70 states 
that no variety is known which is dark fleshed when seedless, but Condit 20 
reports an apparent exception to this rule. 

Variation in seed number is accompanied by differences in composi- 



534 FUNDAMENTALS OF FRUIT PRODUCTION 

tion in many other fruits. In most grape varieties, for instance, seedless 
fruits are much sweeter than seed-containing berries of the same kinds. 
On the other hand, the differences in composition are often negligible. 
There is no general rule that can be laid down stating that seedlessness 
tends either to improve or to detract from quality. 

Season of Maturity. — There is often a considerable difference in the 
time intervals between fruit setting and maturing of seedless and seed- 
containing fruits of the same variety. As a rule the parthenocarpic or 
seedless fruits are slower in reaching maturity than the seed-bearing 
specimens. Munson 98 mentions several instances in which flowers of the 
cucumber, pumpkin and summer squash were induced to set fruit by 
applying to their stigmas pollen of certain other species of cucurbits. The 
resulting fruits which were seedless required over 2 months longer for 
maturity in some cases and in all cases a somewhat longer period than was 
necessary for the development of normal fruits from intra-specific polli- 
nation. The so-called "second bloom" fruits of the apple and pear that 
set 2 to 4 weeks after the usual blossoming period and are very often 
seedless frequently never mature properly and such maturity as they do 
attain is reached only after they have persisted on the trees much longer 
than the extra 2 to 4 weeks that would compensate for their late setting. 
Caprified figs of the Smyrna type drop from the trees at full maturity; 
uncaprified figs tend to persist and usually must be cut or pulled from the 
trees, as they will fall only when past their prime. 40 In the Japanese 
persimmon seed-containing fruits usually ripen earlier. Zengi commonly 
matures its seed-bearing fruits in late July, while its seedless fruits may 
not be ready for harvest until December. 70 In other varieties there may 
be less difference in ripening periods, though they are often quite distinct. 
Fruits bearing only one or two seeds show a tendency to ripen with the 
seedless, while those with a greater number show a tendency to ripen with 
the normal fruits. 70 

In almost all cases the relation of seed number to season of maturity 
is of very secondary importance. 

Specific Influence of Pollen on Resulting Fruit. — Much has been 
said on the supposed specific influence of the pollen on the characteristics 
of the fruit resulting from the pollination. For instance, it has been 
claimed that the red color of striped apple varieties is intensified after 
pollenizing with a dark red sort. The pollination of varieties with 
an acid flesh with pollen from a sweet or subacid variety has been said to 
result in fruit less acid in character. Early maturing sorts are claimed 
to mature their fruits somewhat later if pollinated by late ripening kinds. 
These conceptions are based on a misunderstanding of the processes 
actually involved in pollination, fertilization and fruit development, or 
on faulty observations, or on a wrong interpretation of field observations 
that may have been accurate. 



THE DEVELOPMENT OF THE FRUIT 



535 



There is no evidence to indicate any immediate influence of pollen 
on the color of the resulting fruit, or any direct effect on its composition, 
flavor, quality, shape, season of maturity or keeping quality. This 
statement is borne out by a number of extensive cross and self pollination 
experiments 99 ' 144 as well as by a theoretical consideration of the nature 
of the tissues and processes involved in fruit setting and maturing. Of 
course if in a series of pollination experiments some pollen is used on a 
certain variety and normal seed-containing fruits result and then pollen 
of some other kind is used on other flowers stimulating them to set and 
mature seedless fruit, differences in size, shape, composition and season of 
maturity may be obtained. However, these are diversities associated 
more directly with the relationship existing between seed formation and 
fruit development and not directly between kind of pollen and fruit 
development. In the same way the pollination of pistils of a given 
sort with pollen of half a dozen other varieties with which it is inter- 
fruitful may result in one crossing in fruits averaging say two seeds, in 
another crossing in fruits averaging four seeds, and so on. Under these 
conditions minor differences in size, composition, shape and even flesh 
color and season of maturity may follow. Differences of this kind 
probably account for such inequalities in fruit size in the pear as were 
found by Waite 132 when he used pollen of several kinds on Bartlett or 
Kieffer pistils (see Table 10). 

Table 10. — Influence of Kind of Pollen on Fruit Size and Seed Weight 

in Pears 
(After Waite 132 ) 



Cross 


Average weight 
of fruit, grams 


Average weight 
of seeds, grams 


Bartlett X Bartlett 


100.4 
116.1 
167.7 
133 . 6 
89.4 
114.2 


0.07 


Bartlett X Anjou 

Bartlett X Easter 


0.38 
38 


Bartlett X Angouleme 

Bartlett X White Doyenne 


0.30 
0.27 


Bartlett X Clapp Favorite 


0.32 







The limited data available indicate that these variations are relatively 
unimportant except in comparing cross pollinations with self pollinations. 
That is to say, many varieties that will set and mature fruit when self 
pollinated will set and mature distinctly larger fruits when cross pollinated, 
regardless of the kind of pollen used if only it is from a compatible variety. 
The explanation of the smaller fruits resulting from self pollination 
is that though selfing often results in f ruitf ulness the fruits bear few or no 
perfect seeds, while the cross pollinated fruits have the usual number of 



536 FUNDAMENTALS OF FRUIT PRODUCTION 

good seeds. In other words, it is crossing so as to secure a good comple- 
ment of seeds, rather than crossing with some particular variety, that is 
responsible for the difference in size and is consequently important in the 
orchard. Investigations conducted with many fruits indicate that the 
number or percentage of seeds developing in the fruits of different kinds 
is to a considerable extent a varietal characteristic or at least it is 
more dependent on the variety and the condition of the tree or plant 
than on the kind of pollen, assuming that an adequate supply of good 
pollen is available. 

Kraus 85 has pointed out that the occasional striping of self colored 
fruits of the apple, so often cited as proof of an immediate influence of the 
pollen on the character of the resulting fruit, is in reality a special form of 
bud mutation. Bud mutations of this kind may in many cases be propa- 
gated vegetatively and striped varieties obtained. 

What appears at first as an exception to some of the preceding statements 
has been recorded for the developing fruits of the vanilla. McClelland 92 crossed 
two types of this plant — Vanilla planifolia and the "vanillon" type. "The 
typical well-developed fruit of V. planifolia from a close-fertilized blossom is a 
long slender capsule tapering at the stem end but carrying its fullness well down 
toward the blossom end. It contains thousands of tiny, oily, black seeds. 
. . . The fruits [of the vanillon type] are much thicker and shorter . . . 
and differ in being of a more uniform thickness near the two ends, the blossom 
end frequently being rather tapering. Where to either the V. planifolia or the 
vanillon stigma pollen of the other has been applied a very marked modification in 
the form of the fruit has resulted." These differences in shape apparently are 
associated with the location within the capsule of the ovules that were fertilized 
and develop into seeds. When V. planifolia pollen is used on vanillon 
stigmas, fertilization takes place mainly toward the apical end of the ovary and 
not toward the basal end, while in self pollenized vanillon stigmas fertiliza- 
tion occurs clear to the bottom of the ovarian cavity. On the other hand, the 
pollen tubes of the vanillon type seek the basal ovules in the ovaries of the 
V. planifolia type when that crossing is made. In reality, instead of being an 
exception to the statement that crossing with a particular kind of pollen affords 
no direct influence on the character of the resulting fruit, this is but another 
instance of an indirect effect on shape, the direct relationship being between 
kind of pollen and seed number in the one case and seed number and location 
and shape of fruit in the other. 

Summary. — Ordinarily the development of the carpellary and other 
tissues of the fruit depends on fertilization and the consequent develop- 
ment of seeds from the ovules. In some cases, however, the development 
of the fruit may proceed without an accompanying growth of seeds, or 
even without the stimulus of fertilization. In still other cases develop- 
ment may occur in the absence of pollination. Parthenocarpy is a term 
used to cover those cases of fruit development in the absence of fertiliza- 



THE DEVELOPMENT OF THE FRUIT 537 

tion. Parthenocarpic fruits are usually seedless, though seeds may de- 
velop in them parthenogenetically. Some seedlessness is due to embryo 
abortion after fertilization and therefore is not associated with partheno- 
carpy. Fruits which the botanist classifies as accessory are somewhat 
more inclined to parthenocarpic development than those consisting of 
ovarian tissues only. Parthenocarpy is no insurance, however, against 
loss of crop from excessive dropping of blossoms under certain condi- 
tions. In general, seedlessness is valuable from the commercial stand- 
point. In most instances there is a distinct correlation between -the 
formation of seeds and the development of the fleshy tissues of the fruit — 
the greater the seed number, the larger the fruit. Other limiting factors, 
however, may destroy this correlation. Between seed-containing and 
seedless fruits of the same varieties, there are often distinct differences 
in form, composition and ripening period. However, there is no good 
evidence that the specific qualities or characteristics of the pollen variety 
are in any way stamped upon the resulting fruit. 



CHAPTER XXX 
FRUIT SETTING AS AN ORCHARD PROBLEM 

The preceding discussion has shown that certain fruit varieties are 
completely self fruitful, others are partly self fruitful and still others are 
self barren. With varieties definitely known to be self fruitful it is safe 
to plant solid blocks to a single variety without making any provision 
for cross pollination. The heavy production that characterizes large 
plantations of the Concord grape, the Baldwin apple, the Montmorency 
cherry, the Cuthbert raspberry and many other fruits is sufficient evi- 
dence on this point. On the other hand many varieties that are often 
considered self fruitful because in the average season they set a full crop 
without the aid of any foreign pollen, are often greatly benefitted by 
cross pollination. Thus though the French prune is generally considered 
self fruitful and there are many large orchards consisting exclusively of 
that variety, a higher percentage of its blossoms set when cross pollin- 
ated with Imperial than when selfed. 65 In general it is good practice 
always to make provision for cross pollination when planting the orchard, 
unless there is definite knowledge that this is not needed for the variety 
when grown under the conditions in question. Even though a variety 
is entirely self fruitful under a given set of conditions the evidence shows 
that in many cases the increase in the size of fruit resulting from the 
stimulus of cross fertilization is sufficient to warrant planting together 
two or more varieties which bloom at the same time. 

Fortunately the selection of varieties to secure effective cross pollina- 
tion does not usually add many complications to the problem of variety 
selection. In most fruits the grower prefers to raise two or more varieties 
rather than a single sort. By choosing those that ripen at different 
seasons the harvesting problem is usually greatly simplified and often 
problems of tillage and spraying as well. When the orchard is to be 
planted to two or more varieties for reasons other than cross pollination, 
it is necessary only to make a selection such that their blossoming seasons 
overlap to a considerable extent. When it seems best to have as large 
a part of the orchard as possible consist of a single variety, the problem 
of selecting one for cross pollination purposes is not materially different 
than before. First and foremost, its blossoming season should overlap 
that of the main sort. Then, questions of its maturing season, produc- 
tiveness, market value and so on, should receive due consideration. 
Another point that should receive attention in the selection of a pollenizer 

538 



FRUIT SETTING AS AN ORCHARD PROBLEM 539 

to be planted in limited numbers for the benefit of a main sort is its 
pollen -bearing qualities. Some varieties are heavy pollen producers; 
others bear only limited amounts. Thus Meylan is one of the best varie- 
ties of the English walnut and Glen Mary one of the poorest strawberries 
to plant for pollinating other varieties. 

. The Number of Pollenizers. — The question often is raised as to the 
number or percentage of pollenizers necessary when business considera- 
tions make it desirable to limit them as much as possible. No very 
definite rule can be given. In most deciduous tree fruits every third 
tree in every third row will furnish all the pollen necessary for the remain- 
ing 89 per cent. This proportion, however, would not be practicable in 
the strawberry plantation when it is desired to grow pistillate varieties 
mainly. Much depends on the provision for cross pollinating agents. 
If it is an insect-pollinated plant and pollen-carrying insects are numerous 
(say amounting to one swarm of bees for each 1 or 2 acres of fruit trees) 
fewer trees of the less valuable pollenizers are necessary than if the bees 
are few. 

In cases where large blocks of a single self unfruitful variety have been 
planted and the trees have been in the orchard for a number of years 
much quicker results can be obtained by grafting over some of them than 
by removal and replanting. Occasionally growers solve the difficulty 
by grafting over a limb or two in each tree, but this usually complicates 
the problem of harvesting and from an economic standpoint is less satis- 
factory than changing the entire tops of certain trees. 

Temporary Expedients. — Immediate results are often obtainable in 
self unfruitful orchards through securing from trees of other varieties large 
branches containing numerous flower buds and placing them here and there 
in the self barren orchard. This permits pollen-carrying insects to effect 
a transfer of pollen from these branches to the pistils of the orchard trees. 
Such branches should be cut just as their flowers are starting to open and 
stood in buckets of water so that they will keep fresh while their flowers 
are opening and shedding pollen. This is only a temporary expedient, 
for it is troublesome and often rather expensive; however, it has been the 
means of insuring a good set of fruit in many cases when there would have 
been a crop failure otherwise. It really is a kind of artificial pollination, 
comparable to practices in vogue for thousands of years in the produc- 
tion of dates and many varieties of figs. 

Pollinating Agents. — Wind and insects have been mentioned as the 
chief pollen -carrying agencies for deciduous fruits. Of the two, insects 
are by far the more important except in some of the nut crops. In fact 
the amount of cross pollination effected through the agency of the wind 
in apples, pears, peaches and other insect-pollinated fruits is practically 
negligible. This has been shown experimentally for the plum by 
Waugh 136 and for other fruits by other investigators. Among pollen- 



540 FUNDAMENTALS OF FRUIT PRODUCTION 

carrying insects the common honey bee is probably the most important 
for the fruit grower. Its importance is such that the presence of an 
ample number should be insured during the blossoming season. In 
some of the cherry growing sections of the Pacific Northwest growers 
make a practice of securing colonies of bees from apiarists to place in 
their orchards during blossoming and they find that the rental they 
pay yields them a higher rate of interest on their investment than any 
other item in their cost of production. No hard and fast rules can be 
laid down regarding the number of colonies necessary for effective pol- 
lination in an orchard of a given size. Much depends on the size of the 
trees, their profusion of bloom and the number of hours of favorable 
weather for pollination during their flowering season and the presence 
or absence of other pollen-carrying agents. Ordinarily one colony of 
bees to each 1 or 2 acres of orchard, depending on conditions, will 
produce satisfactory results and sometimes they will take care of a 
considerably larger acreage. 

It is often assumed that perfect flowered and self fruitful varieties 
require no outside agent for the transfer of pollen from stamen to stigma. 
In other words, the self fruitful variety is assumed to be autogamous. 
This is often the case, at least to a certain extent, However, it has 
been found in California that Imperial prune trees from which bees were 
excluded during the blossoming season set only 0.34 per cent, of their 
blossoms, while trees of the same variety accessible to bees but protected 
from cross pollination from other varieties set 3.02 per cent. 65 In 
the French prune 19 per cent, of the blossoms matured fruit where bees 
visited them, while only 0.43 per cent, matured fruit where the bees were 
excluded. Conditions may be quite different in other fruits or in other 
self fruitful varieties of the plum, but in the absence of definite knowl- 
edge that the varieties he is growing are both self fruitful and autogamous 
the grower should make adequate provision for pollen transfer. 

The Fruit Setting Habits of Different Fruits. — In the preceding 
discussion of the factors influencing the setting of fruit most deciduous 
fruit species have been mentioned along with certain others. Following 
are summarized statements of the more important fruit setting character- 
istics of the common fruits. 

Apple. — The flowers of the apple are true hermaphrodites. Occa- 
sionally defective pistils are found and generally a portion of the pollen 
grains are defective, though apparently all varieties mature a certain 
amount of good pollen. 10 The percentage, however, varies with environ- 
mental conditions. Many varieties are self fruitful, many others are 
self barren or partly so. Lewis and Vincent 88 reported about 70 per cent, 
of the varieties studied as self barren in Oregon; Gowen 56 found about 
63 per cent, completely self barren and only 13 per cent, completely self 
fruitful in Maine and Hooper 68 reported about two-thirds of the varieties 



FRUIT SETTING AS AN ORCHARD PROBLEM 541 

he worked with in England to be self sterile. The degree of self fruitf ill- 
ness in the apple varies greatly with the age and vigor of the trees, the 
season, locality and many other factors. Thus the Jonathan, which is 
self fruitful in many parts of the United States, is self fruitful in Victoria 
(Australia) when grown on soils of medium productivity, but self barren 
when grown on rich soils. 44 Among the prominent commercial varieties 
that are classed as comparatively self fruitful, at least in a number of 
sections, are: Baldwin, Ben Davis, Gano, Jonathan, Oldenburg, Yellow 
Newtown, Grimes, Wagener, Yellow Transparent, Willow Twig, Esopus, 
Stark. On the other hand, nearly all of these varieties have been reported 
partly or completely self barren in certain localities or at certain times. 
Among those classed as partly or completely self barren are: Arkansas 
Black, Gravenstein, King, Arkansas, Maiden Blush, Missouri Pippin, 
Rome, Ralls, Rhode Island, Salome, Tolman, Wealthy, Winesap and 
York. These varieties, however, may frequently prove self fruitful. 

Young vigorous trees just coming into bearing have been observed 
repeatedly to be much more likely to drop their fruit than trees of the 
same varieties somewhat older and having the bearing habit well estab- 
lished. On the other hand old weak trees frequently bloom very heavily 
but set little or no fruit. Often this situation can be remedied by liberal 
applications of nitrate of soda or some other quickly available nitrogenous 
fertilizer shortly before blossoming. 

Apple scab and fire blight frequently attack the blossoms or the newly 
set fruits and are responsible for much dropping at an early stage. These 
diseases can be controlled by proper spraying and sanitary measures 
respectively. 

Inter-unfruitfulness has been reported for a few varieties, 56 ' 107 
particularly some of those of the Winesap group; but a large body of 
data indicates that cross sterility is of very little importance in apple 
production. With perhaps the exceptions just noted the grower may 
consider it safe to interplant any one variety with any other for purposes 
of cross pollination, provided they bloom at the same time. 

Parthenocarpy occurs rather frequently, but true parthenocarpic 
varieties are rare. 

Pear. — The flowers of the pear, like those of the apple, are true her- 
maphrodites. So far as known, all varieties produce at least a certain 
amount of good pollen. However, many pear varieties are self barren 
because of self incompatibility. Waite 132 reported 22 out of 36 varieties 
as self unfruitful. Among the more prominent of this group are: Anjou, 
Bartlett, Clairgeau, Clapp Favorite, Columbia, Easter, Howell, Louise 
and Winter Nelis. Among the more important of the self fruitful 
varieties are: Angouleme, Bosc, Flemish Beauty, Kieffer, LeConte, 
Seckel, Tyson and White Doyenne. However, Kieffer has been reported 
practically self sterile in Virginia 47 and Bartlett has been found partly 



542 FUNDAMENTALS OF FRUIT PRODUCTION 

self fruitful in certain localities in California. 130 It has been found 
that most sparingly self fruitful pear varieties generally mature fruits 
with few or no good seeds and that these fruits are distinctly inferior 
in size to those of seed-bearing fruits of the same varieties resulting 
from cross pollination. Pears generally should be so planted as to 
secure the benefits from crossing. 

So far as known the more common pear varieties are interfruitful 
and one variety is as good as another in cross pollination if it blossoms 
at the right period. 

Parthenocarpy is not uncommon in pears but none of the varieties 
of commercial importance in America is parthenocarpic regularly. 

Quince. — Circumstantial evidence points clearly to the conclusion 
that the commonly cultivated varieties of the quince are self fruitful. 
This is supported by the results of investigations of Dorsey in New York 
(data unpublished). 

Peach. — Experimental work with the peach at the Missouri, 143 * 
Delaware, 17 and Virginia 47 Stations indicates that practically all the 
commonly grown varieties are self fruitful. Furthermore there is no 
evidence of any gain in size of fruit from cross pollination. The grower 
is safe, therefore, in planting entire orchards to a single variety. 

Almond. — The work of Tufts 129 has shown that all almond varieties 
that were tested are generally self sterile under California conditions, 
though in occasional seasons certain varieties will set a fairly good crop 
with their own pollen. This self unfruitfulness is due to incompatibility 
rather than to imperfect pollen, for the pollen proves satisfactory on the 
pistils of certain other varieties. Certain varieties were found also to be 
interbarren; I.X.L. and Nonpareil will set practically no fruit when 
interplanted and the same is true for plantings of Languedoc and Texas. 

Plum. — Plum varieties vary greatly in their abilities to mature fruit 
without the aid of cross pollination. Waugh 134 > 135 > 136 > 137 reported 
practically all the commonly cultivated varieties of the Japanese and 
American species to be self sterile; this has been confirmed by the inves- 
igations of others. 52 ' 62 > 64 > 89 > 133 On the other hand, a considerable 
number of European varieties, including Giant, Green Gage, Italian, 
French and Blue Damson have been found partly or completely self 
fruitful in Oregon, 89 and Sutton 125 reported 18 out of 39 varieties to be 
fully self fruitful and five more partly self fruitful in England. 

Hendrickson 64 and Marshall 88 reported all Japanese varieties tested 
as interfruitful and Waugh 135 found both Japanese and American varieties 
generally interfertile. Some exceptions, however, have been recorded. 
Thus Whitaker and Milton, both seedlings of Wildgoose, are interbarren 
and, curiously enough, both are fertile with Sophie; however, Sophie 
used as the pistil parent is fertile with neither. 137 Dorsey 37 obtained 
only eight mature fruits from 1327 flowers of the Compass pollinated 



FRUIT SETTING AS AN ORCHARD PROBLEM 543 

with Yellow Egg, while 114 flowers set and matured fruit when polli- 
nated with Burbank. Though both crosses evidently may be classed 
as interfertile, there is a great difference in the degree of fertility exhibited. 
Marshall, 89 working with varieties of P. domestica, found anyone combina- 
tion to give as good set of fruit as any other; Sutton, 125 working with other 
varieties of the same species, reached the same conclusion, except that 
intersterility appeared in three varieties. However, two of these three 
varieties originated as bud sports from the third. The European plums 
are not interfruitful to any considerable degree with those of either the 
Japanese or American groups. 

Except for certain varieties of the several European groups known to 
be self fruitful, plums always should be planted so they will secure the 
advantages of cross pollination. 

Apparently both self and cross unfruitfulness in the plum is due to 
incompatibilities and not to degeneration of the pollen or of the embryo 
sacs. 

Apricot. — Experimental data are not available on the pollination 
responses of the apricot; however, circumstantial evidence indicates 
that at least a number of the leading varieties grown in America are 
self fruitful. 

Cherry. — Until a comparatively recent time cherries have been 
assumed to be self fruitful. In 1915, Gardner 50 reported several varieties 
of the sweet cherry, all that were tested, as self unfruitful under Oregon 
conditions and a little later Tufts 128 reported a number of the same 
varieties self barren in California. All the sweet cherries tested have been 
reported self barren in England. 125 The conclusion seems warranted 
therefore that self barrenness is the general rule in this group. Gardner 50 
also found May Duke self unfruitful in Oregon, but Sutton 125 found 
both May Duke and Archduke partly self fertile and Late Duke fully 
self fertile in England. Experimental data on the sour cherries are not 
available but Hedrick 61 concludes from his observations that self fruit- 
fulness is the general rule in that group. 

Inter-unfruitfulness has been found among some of the varieties of 
the sweet cherry — notably Napoleon, Lambert and Bing — in both 
Oregon 50 and California. 128 

Self unfruitfulness and cross unfruitfulness in the cherry are due to 
incompatibilities rather than to any structural defects of pollen or ovules. 

Grape. — As mentioned already, conditions in the grape range all the 
way from complete self fruitfulness to complete barrenness. Varieties 
of hybrid origin particularly are likely to be self barren, though this 
condition is found in many varieties descended from a single species. 35 ' 36 
Among some of the more common self fruitful varieties may be men- 
tioned: Clinton, Champion, Concord, Isabella, Moore Early, Niagara, 
Worden, Agawam, Catawba, Delaware, Diamond and Norton. Among 



544 FUNDAMENTALS OF FRUIT PRODUCTION 

those that are self unfruitful are: Salem, Barry, Brighton and the follow- 
ing are among those often at least partly self fruitful : Lindley, Vergennes, 
Wyoming. 3 

Practically all the varieties of the Muscadine group bear pseudo- 
hermaphroditic flowers and should have staminate vines interplanted 
with them. 

The immediate factor responsible for self barrenness in the grape is the 
production of impotent or sterile pollen which is incapable of fertilizing 
the ovules of the same or of any other variety. 9 ' 36 Consequently self 
barren varieties are interbarren and partly self barren sorts are partly 
interbarren. Self fertile varieties should be interplanted with the self 
barren or partly self barren kinds. The production of impotent or 
sterile pollen is associated almost invariably with curved or reflexed 
stamens; good pollen is produced in erect stamens. This flower character 
therefore affords an accurate index to the degree of self fruitfulness that 
may be anticipated, except in the comparatively few parthenocarpic 
varieties. 

Many grape varieties occasionally produce a few seedless berries 
when not pollinated or when pollinated with impotent pollen. This 
characteristic apparently is aided by certain practices such as ringing or 
girdling. In a few varieties, such as Thompson's Seedless, this occurs 
regularly. 55 According to Stout, 123 seedless American grape varieties 
generally produce good pollen, but since their "femaleness" is not 
strongly developed they are not able to mature good seeds. 

Strawberry. — Strawberry varieties are generally classed as pistillate 
flowering and perfect flowering. Apparently all the perfect flowering 
sorts produce good pollen and all are self fruitful and apparently any 
perfect flowering variety may be planted with any pistillate flowering 
sort for purposes of cross pollination. Since, however, some of the per- 
fect flowering varieties produce only small amounts of pollen, they are 
not ideal pollenizers for pistillate sorts. In general the later maturing 
flowers of the inflorescence, particularly in the perfect flowering varieties, 
are less fertile than earlier flowers of the same cluster and this pistil 
sterility is "expressed in the production of irregularly shaped berries or 
entirely sterile flowers." 131 

Currant and Gooseberry. — Few exact data are available on the polli- 
nation requirements of the currant and the gooseberry. However, field 
observation indicates clearly that the varieties commonly grown in this 
country are self fruitful and hence no provision need be made for cross 
pollination. Hooper 68 has reported all the varieties of the English goose- 
berry which he tested to be self fertile. 

The Brambles. — Until comparatively recent date the bramble fruits 
have generally been considered self fruitful. Hooper, 68 working with a 
number of varieties of the raspberry and with the loganberry in England, 



FRUIT SETTING AS AN ORCHARD PROBLEM 545 

found all that he tested self fertile but reported some increase in size 
of fruit resulting from cross pollination. In North Carolina 11 out of 
15 varieties of dewberries were found self barren and 12 out of 16 varieties 
of blackberries self fruitful. The varieties of Rubus villosus generally 
were self fruitful, those of R. trivialis self barren. There was no increase 
in size of fruit from cross pollination in those varieties maturing fruit 
when selfed. The Vineland (Ontario) Horticultural Experiment Sta- 
tion 111 has reported that a number of the seedlings of the raspberry which 
they have obtained in their breeding work are self sterile. Others are 
self fruitful or partly so. A number of the blackberry-dewberry hybrid 
varieties are partly or wholly self barren. 

The Nuts. — Data are not available on the degree of self fruitfulness 
characteristic of different varieties of the walnut, pecan, hickory, chest- 
nut and filbert. All are monoecious and a large majority are characterized 
by partial dichogamy. In some the dichogamy is almost complete, 
rendering the tree or variety self unfruitful to a marked degree. To 
what extent, if at all, individual trees or varieties are self unfruitful because 
of incompatibility is not known. On account of the partial dichogamy 
that is generally found it is always a good plan to interplant two or more 
varieties having approximately the same blossoming seasons. 

Persimmon. — The kaki, or Japanese persimmon, includes varieties 
bearing pistillate flowers only and those bearing both pistillate and stami- 
nate flowers. Of the varieties in the latter class some bear staminate 
flowers regularly, others bear them sporadically. The names pistillate 
constants, staminate constants and staminate sporadics have been applied 
to these several groups. 

Some varieties set fruit freely without pollination and they mature 
seedless fruits. Others require pollination and their fruits usually con- 
tain one or more seeds. Apparently pollination is not so essential to the 
securing of a good persimmon crop in California as in Florida. 20 

The differences in the size, shape, color, flavor and season of maturity 
of seed-bearing and seedless persimmons have been discussed previously. 

There is reason to believe that most pistillate flowers of the native 
American persimmon (Diospyros virginiana) require pollination from 
staminate trees of the same species in order to set and mature a good crop. 
The Japanese and American varieties of persimmon are not interfruitful. 72 

Summary. — In the absence of definite knowledge that the variety 
being planted is self fruitful under local conditions provision should 
always be made for cross pollination. Even when varieties are self 
fruitful the increase in size often obtained as a result of cross pollination 
warrants the use of other pollenizers. In most tree fruits one of the 
pollenizing variety is sufficient for 8 or 10 trees of the leading sort. 
Top grafting and the use of flowering branches of other varieties at the 
blossoming season are the most satisfactory methods of providing for 

35 



546 FUNDAMENTALS OF FRUIT PRODUCTION 

cross pollination in established self unfruitful or inter-unfruitful orchards. 
Insects, particularly the honey bee, are the most effective pollinating 
agents in the deciduous fruit plantation. There should be ample provi- 
sion for pollen transfer, even in orchards of self fruitful varieties. The 
fruit setting habits and pollination requirements of different deciduous 
fruits are discussed. 

Suggested Collateral Readings 

Waite, M. B. Pollination of Pear Flowers. U. S. D. A. Div. Pom., Bui. 5. 1895. 
Hedrick, U. P. Relation of Weather to the Setting of Fruit. N. Y. Agr. Exp. Sta. 

Bui. 299. 1908. 
Valleau, W. D. A Study of Sterility in the Strawberry. Jour. Agr. Res. 12:613- 

670. 1918. 
Dorsey, M. J. Pollen Development of the Grape with Special Reference to Sterility. 

Minn. Agr. Exp. Sta. Bui. 144. 1914. 
Eisen, G. The Fig. U. S. D. A. Div. Pom., Bui. 9. Pp. 74-128. 1901. 

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25. Ibid. 2: 115-117. 

26. Ibid. 2: 119. 

27. Ibid. 2: 147. 



FRUIT SETTING 547 

28. Ibid. 2: 152-153. 

29. Ibid. 2: 165-169. 

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61. Hedrick, U. P. Cherries of New York. P. 83. Albany, 1915. 

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74. Husmann, G. C, and Dearing, C. U. S. D. A. Farmers' Bui. 709. 1916. 



548 FUNDAMENTALS OF FRUIT PRODUCTION 

75. Johnson, D. S. Carnegie Inst, of Wash. Pub. 269. 1918. 

76. Kerner, A., and Oliver, F. W. Natural History of Plants. 2(1): 407-414. 

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77. Ibid. Pp. 104-129. 

78. Ibid. Pp. 312-313. 

79. Ibid. P. 317. 

80. Ibid. P. 420. 

81. Ibid. P. 453. 

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87. Kusano, S. Jour. Coll. Agr. Imp. Univ. Tokio. 6: 7-120. 1915. 

88. Lewis, C. I., and Vincent, C. C. Ore. Agr. Exp. Sta. Bui. 104. 1909. 

89. Marshall, R. E. Proc. Am. Soc. Hort. Sci. 16: 42-49. 1919. 

90. Massart, J. Bui. Jard. Bot. Brux. 1: 85-95. 1902. 

91. Mathewson, C. A. Torrey Bui. 33: 487-493. 1906. 

92. McClelland. Jour. Agr. Res. 16: 245-251. 1919. 

93. Millardet, A. Rev. de Viticulture. 16: 677-680. 1901. 

94. Miyoshi, M. Bot. Zeit. 52: 1-28. 1894. 

95. Mottier, D. M. Carnegie Inst. Wash. Pub. 15: 174-180. 1904. 

96. Miicke, M. Bot. Ztg. 66: 1-23. 1908. 

97. Muller-Thurgau, H. Landw. Jahrb. Schweiz. 22: 564-597. 1908. 

98. Munson, W. M. Me. Agr. Exp. Sta. Ann. Rept. Pp. 29-58. 1892. 

99. Ibid. Pp. 218-229. 1898. 

100. Osawa, I. Jour. Coll. Agr. Imp. Univ. Tokio. 4: 83-116. 1912. 

101. Ibid. 4: 237-264. 1913. 

102. Parrott, P. J., Hodgkiss, H. E., and Hartzell, F. Z. N. Y. Agr. Exp. Sta. Tech. 

Bui. 66. 1919. 

103. Paton, J. B. Doctor's Dissertation. Yale University. 1920. 

104. Popenoe, P. B. Date Growing. P. 113. Altadena, Cal. 1913. 

105. Ibid. P. 105. 

106. Popenoe, W. U. S. D. A. Bui. 542. 1917. 

107. Powell, G. H. Del. Agr. Exp. Sta. Ann. Rept. 12: 129-139. 1900. 

108. Price, W. A. Purdue Univ. Agr. Exp. Sta. Bui. 247. 1920. 

109. Reed, H. S. Jour. Agr. Res. 17: 153-165. 1919. 

110. Reimer, F. C, and Detjen, L. R. N. C. Agr. Exp. Sta. Bui. 209. 1910. 

111. Rept. Vineland (Ont.) Hort. Exp. Sta. P. 17. 1919. 

112. Rixford, G. P. U. S. D. A. Bui. 732. 1918. 

113. Sandsten, E. P. Wis. Agr. Exp. Sta. Ann. Rept. 22: 300-314. 1905. 

114. Sandsten, E. P. Wis. Agr. Exp. Sta. Res. Bui. 4. 1909. 

115. Schuster, C. E. Bienn. Crop Pest and Hort, Rept. Ore Agr. Exp. Sta. 3: 44-46. 

1921. 

116. Shoemaker, D. M. Johns Hopkins Univ. Circ. 21: 86-87. 1902. 

117. Sirks, M. J. Arch. Neerland. Sci. Ex. et Nat. (Ser. B). 3: 205-234. 1917. 

118. Stevens, N. E. Bot. Gaz. 53: 277-308. 1912. 

119. Stewart, F. C, and Eustace, H. J. N. Y Agr. Exp. Sta. Bui. 200. 1901. 

120. Stout, A. B. Mem. N. Y. Bot. Garden. 6: 333-454. 1916. 

121. Stout, A. B. Am. Jour. Bot. 4: 375-395. 1917. 

122. Stout, A. B. Jour. Genetics. 7: 71-103. 1918. 



FRUIT SETTING 549 

123. Stout, A. B. N. Y. Agr. Exp. Sta. Tech. Bui. 82. 1921. 

124. Stuckey, H. P. Ga. Agr. Exp. Sta. Bui. 124. 1916. 

125. Sutton, I. Jour. Genetics. 7: 281-300. 1917-18. 

126. Swingle, W. T. U. S. D. A., Bur. PI. Ind. Bui. 53. 1904. 

127. Trabut, L. Jour. Heredity. 7: 416. 1916. 

128. Tufts, W. P. Cal. Agr. Exp. Sta. Ann. Rept. P. 46. 1916. 

129. Tufts, W. P. Cal. Agr. Exp. Sta. Bui. 306. 1919. 

130. Tufts, W. P. Cal. Agr. Exp. Sta. Bui. 307. 1919. 

131. Valleau, W. D. Jour. Agr. -Res. 12:613-670. 1918. 

132. Waite, M. B. U. S. D. A., Div. Pom. Bui. 5. 1895. 

133. Waite, M. B. Amer. Agric. 75: 112. 1905. 

134. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 10: 87-93. 1896-1897. 

135. Ibid. 11:245. 1897-1898. 

136. Ibid. 13:358. 1899-1900. 

137. Waugh, F. A. Plums and Plum Culture. Pp. 282-307. New York, 1901. 

138. Webber, H. J. U. S. D. A., Div. Veg. Phys. and Path. Bui. 22. 1900. 

139. Wellington, R. Am. Nat. 47: 279-306. 1913. 

140. Wester, P. J. Torrey Bui. 37: 529-539. 1910. 

141. White, J. Ann. Bot. 21: 487-499. 1907. 

142. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 46. 1899. 

143. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 117. 1914. 

144. Wicks, W. H. Ark. Agr. Exp. Sta. Bui. 143. 1918. 



SECTION VI 
PROPAGATION 

The universality of variation in plants when propagated sexually is well 
known. Comparatively few are the fruit plants which reproduce their 
like by seed with any great degree of certainty. Though this condition 
has certain disadvantages it is, on the whole, fortunate. The animal 
breeder or the breeder of seed propagated plants, when he has obtained a 
desirable individual, confronts the problem of reproducing its like, of 
fixing the strain. The propagator of fruit plants facing the same prob- 
lem has a different solution ; from the parent plant he cuts pieces each of 
which produces a plant practically the same as the original. The problem 
of propagation of fruit plants is essentially making these pieces of the 
parent plant live. Sometimes they grow if thrust into earth; hence, 
propagation by cuttings. Again, they must be placed on rooted plants 
with which they can unite; hence, budding and grafting, which is in reality 
the placing of cuttings is another medium. 

Though the conception is simple, actual practice involves a seemingly 
interminable variety of refinements and detail, varying with the climate, 
the species, even the variety and with economic conditions. The mere 
feasibility of a given process does not demonstrate its expediency and 
though the process is expedient it does not necessarily follow that the 
product is of lasting value. A certain stock may be desirable to the 
nurseryman because it is cheapest, or most easily worked or makes the 
best initial growth and still it may not be well suited to the orchard. 
This condition may be reversed. Again, a given stock may be entirely 
satisfactory if the trees are planted in one section or in one soil and totally 
unsuited to another section or to another soil. 

Though the art of grafting (the term as used in this discussion in- 
cludes budding) apparently antedates the art of writing, many questions 
growing out of its application are far from answered, at least so far as 
American practice is concerned. In the early days of standardized apple 
production, when the seedling orchards were newly topworked to named 
varieties, there was much discussion of the effect of stock on cion and of 
related questions, but attention was soon diverted to the protection of 
fruit and trees from pests and for many years little notice has been given 
the underground parts of the trees, except when it was forced upon 
growers in some sections. With the rise of commercial nurseries the 

550 



PROPAGATION 551 

newer generation of fruit growers know little about the propagation of the 
trees they grow; many do not know on what stocks their trees have been 
worked. 

Similarly, scientific investigation has devoted little attention to these 
matters, being concerned with perhaps more pressing problems. For 
most of the precise study in this field indebtedness must be acknowledged 
to European workers. 



CHAPTER XXXI 
THE RECIPROCAL INFLUENCES OF STOCK AND CION 

Grafts between certain plants are successful; in many other cases the 
results range from partial success to utter failure. Sometimes there is 
immediate failure to unite; sometimes the grafts unite but the death of 
either cion or stock — generally the cion — occurs in a short time; again 
the grafted parts may unite but there will be an ultimate failure in stock 
or in cion. On the other hand, as with apricot on plum and on peach in 
New York, plants may live a considerable time and function fairly well, 
under favorable conditions, without a very successful union of stock and 
cion and it is only an untoward incident, such as a high wind, that reveals 
the defective union. Sometimes a certain combination can be made 
with one kind of graft and not with others — the approach graft frequently 
succeeds when others fail. Finally, though a certain combination of 
stock and cion may be successful it is not inevitable that a reciprocal 
combination will succeed. 

The capricious occurrence of successful and of unsuccessful combina- 
tions in grafting follows no well defined law. Jost 86 states the cases 
must be accepted as they occur; they are not to be explained. Daniel 50 
explains most of them by the degree of correspondence of "functional 
capacity" of stock and cion, i.e., that there must be, for a successful 
graft, a certain relative similarity, qualitatively and quantitatively, in 
their requirements for water and food and in their general habits of 
growth. 

Botanical relationship, as understood by closeness in the system of 
classification, is a fair guide to probable congeniality but it is by no means 
infallible. Horticultural varieties of exogenous plants generally may be 
intergrafted freely, species somewhat less so, genera only occasionally 
and families only rarely. Nevertheless, the pear and the apple form a 
less congenial combination than the pear and the quince though the 
pear is more closely related to the apple than to the quince. Sahut 129 
states that the pear works on quince more readily than Portugal quince 
on quince. 

THE CONGENIALITY OF GRAFTS 

Shoots of potato succeed better on Datura and Physalis than on 
many species of the genus Solarium. According to Sahut 128 Carriere 
grafted Garrya elliptica Dougl. on Aucuba japonica, thus uniting members 

552 



THE RECIPROCAL INFLUENCES OF STOCK AND CI ON 553 

of different families. Biffen 21 succeeded in grafting Trifolium pratense 
on Anthyllis vulneraria, of a different genus. 

Dawson 57 cited some interesting cases: "The Photinia allied to the 
beam tree (Pyrus Aria) and the Eriobotrya [loquat], allied to the medlar, 
both evergreens, will graft on the medlar and not on the hawthorn. 
Cotoneasters, amelanchiers and Pyrus Aria all do well on hawthorn and 
last longer but make slower growth than on mountain ash. Pyrus 
arbutifolia grafts well as a standard on mountain ash. . . . Pyrus 
Toringo . . . will grow on seedlings but are better on Pyrus baccata." 

Manning 105 listed several cases of incompatibility in close relatives. 
The laburnum, he stated, would not take on locust. Flowering dogwood 
on cornelian cherry (both in the genus Cornus) made only short-lived 
unions. The Josika lilac was said to succeed on the ash while the Persian 
lilac failed, though it grew on the common lilac. Coulter 43 states that 
Prunus Padus and P. Laurocerasus show a lack of affinity. Native, Japa- 
nese and European plums take readily on western sand cherry, though 
sweet and sour cherries unite with it much less readily. 67 

The gooseberry will grow on Ribes aureum but not on the cultivated 
edible currants. 33 Some varieties of pears unite readily with quince 
stocks, but others are so conspicuously defective in uniting that thej'- 
necessitate a resort to double working. 

Berckmanns 20 reported that Labrusca and Aestivalis grapes inter- 
worked readily but that, apparently because of the difference in the 
texture of the wood, Labrusca varieties would not take on Vulpina. 
Bioletti 22 recognizes certain of the Vinifera group of grapes as having 
"defective affinity" in that they do not unite at all well with the stocks in 
common use; he recommends a special stock for these varieties because it 
makes an excellent union with them. Among these varieties he lists 
Emperor, Ferrara, Cornichon, Muscat, Mataro, Folle Blanche, Pinot, 
Gamay, Gutedel; the stock recommended for them is known as 1202. 

Brown 28 cites a case in California in which both cion and stock grew 
larger than their customary size. "Almonds grafted on peaches," he 
states, "have developed a circumference of a little less than 10 feet, while 
the maximum size of either, growing alone, would be scarcely 5 feet. 
Where almonds are grafted on plum stock, the reverse is true." Measure- 
ments are cited showing, in the almond on peach, a circumference of 9 
feet 1 inch above the graft and 10 feet 4 inches below, while the almond 
on plum, of equal age with the first combination, measured 4 feet below 
the union and 4 feet 10 inches above. 

Other stone fruits exhibit similar capriciousness. In Vermont the 
Newman plum seemed to have much greater affinity for peach roots than 
did. Green Gage, Stoddard, Chabot or Milton; in fact the last three did 
very poorly on peach stock. 139 In California certain prunes, including 
Robe de Sargent, Imperial Epineuse and Sugar, lack affinity for the 



554 FUNDAMENTALS OF FRUIT PRODUCTION 

peach root; on the almond the last two take well but the first is again 
refractory. 124 The Yellow Egg, Jefferson and Washington plums also 
lack affinity for peach roots. 124 Wisker 156 adds Diamond and Grand 
Duke to this list. Sugar, mentioned above as failing on peach, succeeds 
on apricot, while the French prune fails on the latter stock. 81 

Swingle 140 calls attention to the lack of compatibility between the 
Satsuma orange and the sour orange stock. On the sweet orange, growth 
is satisfactory but the fruit is poor; by far the best results are secured on 
trifoliate stock. The kumquat unites with the sour orange but dies 
after starting growth, though on trifoliate stock it gives very satis- 
factory results. Bonns 26 reported the trifoliate to be distinctly dwarfing 
for lemon, much more so than for orange. 

Apple varieties show various degrees of congeniality with dwarfing 
stocks. Hedrick 75 reported Mcintosh, Wealthy and Lady to be the most 
congenial of a large number of varieties tested, and Jonathan, Esopus, 
Grimes, Alexander, Wagener, Boiken and Bismark as "very satisfactory." 
Baldwin, Rhode Island, Rome, Ben Davis and Northern Spy were uncon- 
genial and Twenty Ounce gave the poorest results. 

Mcintosh 134 is said to make a strong growth as a young tree on cion- 
rooted Transcendent Crab, though Red Astrachan is markedly dwarfed 
on the same stock. 

Maynard 107 described a case which may be considered to have a 
bearing on the present question. It was reported as follows: "About 
10 years ago six small trees of yellow Siberian crab and three of Williams' 
Favorite were planted as represented in the following diagram, S indicat- 
ing Siberian crab, S.B. the same budded and W Williams' Favorite; 

S W S.B. S W S.B. S W S.B. . 

"The trees were all of the same size as nearly as could be selected 
and every third tree in the row was top-budded with the Williams' 
Favorite. The buds all grew well the first season, but the subsequent 
growth was very little and at the end of 10 years all were dead. ■ The 
diameters of the three Siberian crabs were 4, 4}^ and 6 inches, of the three 
Williams' Favorite 3%, 3 and 3 inches, while none of the budded trees 
reached over % of an inch." It is difficult to decide whether this is a 
case where the cion influences stock or stock influences cion but the fact 
is worthy of record here. 

Reciprocal or inverse grafts are not always equally successful. This 
may be due in part to lack of adaptability rather than to a lack of affinity, 
but there appears at times to be a real lack of congeniality in a graft 
whose opposite is congenial. In some of Daniel's work the grafts of 
pimento on tomato seemed rather less successful than those of tomato on 
pimento. 55 Sahut 127 states that the Mahaleb succeeds as a cion on no 
other cherry though it is the standard stock for the sour cherry in America 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 555 

and that the pear does better on the apple than the apple on the pear. 
Baltet states that medlar does well on quince but the quince fails on 
medlar; the same holds true with quince on hawthorn and vice versa. 
Sweet cherry on sour cherry is more successful than the reverse 
combination. 95 

Tufts states: " . . .it has been the experience of certain growers 
in the Vacaville section, California, that practically all the varieties of 
Japanese plums will work satisfactorily with domestica varieties. How- 
ever ... the insertion of European plum scions on Japanese plums 
does not always result in a satisfactory union. It has been found that 
plum orchards, where worked over to Japanese varieties, could not be 
worked back to European varieties unless all the Japanese wood was 
taken from the tree." 143 

Similar contrasts in reciprocal grafts occur in the combination of 
various evergreen on deciduous plants. There are numerous instances 
of at least passable success in grafts of this sort, but the inverse combina- 
tion, deciduous on evergreen, is almost invariably a failure. 

Congeniality and Adaptability Distinguished.— Distinction should be 
made between congeniality and adaptability. The former term refers 
to the degree of success of the union between stock and cion ; the latter 
term to the relation of the combined parts to environment, most often 
to soil and climate. Husmann's conception of perfect congeniality 
in grapes is a condition in which "a variety grafted on another behaves as 
if the stock were grafted with a scion of itself, the union being perfect and 
the behavior of the vine the same as that of an entire ungrafted plant." 83 
He states also, "When both stock and scion are suited to the conditions, 
but will not thrive when grafted, congeniality is lacking." Further: 
"The adaptability of varieties to soil, climates and other conditions can 
often be closely forecasted, but congeniality has to be determined by 
actual test." 

Congeniality and adaptability are sometimes differentiated only 
with difficulty, as is shown by the following quotation from Blunno: 25 
"In France, however, it was found that the yield of the French vines 
grafted on du Lot was low; our experience is exactly the same at the 
Viticultural Station, Howlong [New South Wales] — the wine-grape 
varieties grafted on this stock are the poorest croppers of all. In Sicily, 
however, the affinity between the native European vines and the Rupe- 
stris du Lot seems to be perfect and the yield is heavy. In this state the 
principal wine-grapes are French varieties and this explains how our ex- 
perience with vines on Rupestris du Lot as poor croppers is similar to 
that in France." 

The most congenial combination is not necessarily the most successful, 
as is shown by an experience in New York, citied by Bailey. 7 Plum 
and peach stocks failed to make satisfactory unions with the apricot 










Russian apricots and plums. 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 557 

breaking off, death being due to the failure of the roots to receive enough 
elaborated food from above, though the tops seemed not to suffer greatly 
till the root systems collapsed. Paul C. Stark reports the peach a much 
better stock for apricot than plum. In California there appears to be 
little difficulty in effecting union between apricot cion and peach or plum 
stock, but the almond stock proves recalcitrant. 154 In France certain 
plum stocks are used in the north but farther south success is attained 
with almond, apricot and peach stocks as well as plums. Evidently 
the same difficulty is experienced with almond stock near the Mediter- 
ranean, for Baltet described a double working when this stock was 
used. 10 

From India is reported an interesting case. Brown, 30 trying 
numerous stocks for Malta and Satsuma oranges, found extraordinary 
differences in the behavior of the same variety on different stocks and 
of the same stock worked to different variaties. For the Malta orange 
the "rough lemon" gave greatest vigor and fruitfulness, the "sweet 
lime" was suitable only to amateur growing, producing a small tree with 
a few oranges of high quality, while the citron and sour orange were 
unsuitable. On the other hand the Satsuma orange gave best results 
on the sweet lime; the rough lemon and citron proved unsuitable. 
Figures 56, 57 and 58 show clearly differences associated with the influ- 
ence of stock on cion and of cion on stock. It is noted by Brown that 
his results are not in accord with American experience, particularly in 
the poor growth with the sour orange as a stock for the Malta orange. 
The Satsuma on the same stock was satisfactory, completely reversing 
the results obtained in California. 

This situation seems analagous to that just outlined for grapes and 
suggests that adaptability and possibly congeniality may be operative 
in producing these striking differences and contradictions. 

THE INFLUENCE OF STOCK ON CION 

The recognition of dwarfing stocks is assertion of the effects of the 
stock on the cion; the recognition of the utility of grafting is acquies- 
cence in the independence of the cion. At first glance the question 
seems to hang on both horns of the dilemma. 

Stature. — At the outset the dwarfing effects of certain stocks, such 
as the quince on the pear, the Paradise and Doucin apples on the standard 
apples, the Sand Cherry on plums and sundry others must be conceded 
as evidence of the effect of the stock on the cion. 

Parenthetically it may be stated that much of the conflicting evidence con- 
cerning quince stock is due to the different kinds of quince used. Barry, as 
early as 1848, noted a mixing of quince stocks as received from French nurseries. 16 
Apparently in England at present the situation is very much confused. 71 



558 



FUNDAMENTALS OF FRUIT PRODUCTION 



of the top which > he sto^XrtLT^S.^: X 







however, exceptions and qualifications. Northern Snv ,W ■ 
grower, tends somewhat +„ ^ * ^ounem fepy, itself a vigorous 

roots.." taeS t . 1 T Dy ° ther Va ™ ties w ° rke ° »n its 
=ome vanet.es of apple form eharacteristieally small trees, 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 



559 



while others assume large stature, both worked on similar stock. Certain 
dwarf varieties of peach remain dwarfed regardless of the stock on which 
they are worked. 

On the other hand, some plants attain greater size on roots other 
than their own. The common lilac is said to be greatly increased in 
stature on the ash, though this is a short lived graft. Similar increases 
are said to obtain when Pinus Gerardiana is worked on P. sylvestris, 
incense cedar on common cedar 130 and in herbaceous grafts, as in 
Phy salts on potato, Arabis albida (rock cress) on Brassica oleracea 
(cabbage, etc.,) and Solatium dulcamara (bitter-sweet) on S. lycopersicum. 

Rose acacia is considered to grow larger on Robinia viscosa; likewise 




Fig. 58. — Influence of stock on cion. Left, "Malta" orange on C. Aurantium, sour 
orange ("khatta" of India); right, same on C. Limonum, rough lemon ("kharna" of India). 
Twenty-seven months planted. (After W. Robertson Brown. 30 ) 

the dwarf double-flowering, almond on peach. 106 Magnolia glauca 
(swamp bay) is reported to attain three times its normal size when 
grafted on M. acuminata (cucumber tree), though this has been suggested 
as due to the lack of adaptation to ordinary soil in the root of the former, 
which is a bog plant. 

It is stated that Grimes and Winesap apples increase in vigor when 
worked on vigorous stocks. 112 A similar influence is exercised by 
American persimmon on Japanese persimmon cions. 82 Prunus pumila 
(sand cherry) makes an increased growth on plum stock. 52 Among 
growers of Vinifera grapes the Rupestris St. George (du Lot) stock is 
generally known to induce unusually vigorous growth in varieties worked 
upon it and skilful vignerons recognize this difference when pruning. 

Hedrick 73 reports an experiment in which a number of grape 
varieties more or less grown in the grape regions of New York were studied 



560 



FUNDAMENTALS OF FRUIT PRODUCTION 



on three stocks; Clevener, a Labrusca-Riparia hybrid, grown in New 
York as a direct producing wine grape, Rupestris St. George (or du Lot), a 
stock obtained through California from France and Riparia Gloire, also 
a repatriated American. It should be borne in mind that all the cion 
varieties are commonly grown in this section as direct producers, i.e., 
on their own roots. In almost every case at least one of the stocks used 
caused a marked increase in vigor over that of the cion variety on its 
own roots. Table 1, condensed from Hedrick's data, shows the growth 
ratings of several varieties as direct producers and on the various stocks. 
This growth rating should be distinguished from total growth since 
Hedrick states distinctly that the grafted made less wood growth than 
the ungrafted vines. 

Table 1. — Relative Growth Rating of Grape Varieties on Different Stocks 

in 1910 

(After Hedrick' 12 ) 



Variety 


Own roots 


St. George 


Gloire 


Clevener 


Brighton 


55.0 


56.0 


73.7 


75.0 


Campbell 


17.3 


62.1 


54.6 


35.0 


Catawba 


40.0 


74.0 


70.0 


81.6 


Concord 


46.0 


94.0 


90.7 




Delaware 


46.0 


60.0 


68.7 


81.6 


Herbert 


64.6 


87.5 


87.1 




Iona 


26.8 
53.9 


45.6 
84.5 


43.0 
57.5 




Niagara 


56.4 


Vergennes 


44.1 


77.8 


69.2 


90.3 


Worden 


26.1 


36.0 


61.6 


38.1 






Average 20 varieties 


40.0 


63.2 


65.2 


67.9 



In general, when a symbiotic relation between stock and cion exists at 
all, there is apparently a tendency toward a balance between the two. 
The influence is relative. A dwarfing stock is dwarfing because of the 
limitations on its development relative to the top. There is nothing 
inherent which impels it to dwarf all tops worked on it. As an example 
the quince may be considered. It obviously dwarfs pears in general, 
yet it is said to increase the vigor of Crataegus glabra Thunb. 128 while its 
dwarfing effect on the loquat is slight or absent. 41 

Form. — Closely related to vigor of growth, possibly interwoven with 
it, is form or habit of growth. According to Loudon, 101 "Cerasus canaden- 
sis" naturally a rambling shrub, assumes an upright habit when grafted 
on the common plum, while Tecoma radicans on catalpa forms a round 
head with pendent branches. Garry a elliptica, Sahut states, 130 grafted 
on Aucuba branches less. Chamcecyparis obtusa pygmcea, according to 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 561 

Burbidge, 36 worked on C. Boursieri, grows erect, while on Biota or Thuya, 
or if grown from cuttings, it spreads horizontally on the ground. The 
same writer quotes Briot to the effect that the Libocedrus tetragona is 
changed from a narrow cylindrical column to a wide-spreading form by 
working on Saxegothcea. 

Among fruit plants, the plum and peach have been cited as showing 
in the habit of their tops the influence of the stocks on which they are 
growing. 

Knight 89 described this influence: "The form and habit which a 
peach tree of any given variety is disposed to assume, I find to be very 
much influenced by the kind of stock on which it has been budded; if 
upon a plum or apricot stock, its stem will increase in size considerably, 
as its base approaches the stock, and it will be much disposed to emit 
many lateral shoots, as always occurs in trees whose stem tapers consider- 
ably upwards: and, consequently, such a tree will be more disposed to 
spread itself horizontally, than to ascend to the top of the wall, even when 
a single stem is suffered to stand perpendicularly upwards. When, 
on the contrary, a peach is budded upon the stock of a cultivated variety 
of its own species, the stock and the budded stem remain very nearly 
of the same size at, as well as above and below, the point of their junction. 
No obstacle is presented to the ascent, or descent, of the sap, which 
appears to ascend more abundantly to the summit of the tree. It also 
appears to flow more freely into the slender branches, which have been 
the bearing wood of preceding years; and these extend themselves very 
widely, comparatively with the bulk of the stock and large branches." 

Comparing the growth of the Milton plum on various stocks, Waugh 149 
reported: "The trees of this variety growing on Wayland roots are 
upright narrowly vase-form, with relatively few large branches. They 
are almost as narrow headed as typical trees of Abundance or Chabot. 
On Marianna roots, in the very next row, the trees of Milton are low, 
round-headed, bushy, with thick-spreading, drooping tops, much like 
trees of Marianna. If anything, they exaggerate the typical character 
of the Marianna head. Moreover, the leaves are several shades darker 
and glossier and the twigs are dark red instead of being green as in trees 
of the same variety growing on Wayland roots. On Americana Milton 
has almost the same characters as on Wayland." 

Somewhat later Stewart, 139 describing these same trees, wrote: "At the 
present time the differences in color of foliage and bark of young twigs are not 
noticeable, neither is the ' upright narrowly vase-form ' head of Milton on Way- 
land anywhere near so pronounced. Notwithstanding these modifications, how- 
ever, there is still a marked difference in the habit of growth of the trees upon 
Wayland and Marianna stocks. On Wayland the habit of growth is more or 
less upright, whereas on Marianna the head is low, bushy and spreading. Doubt- 
less, as the trees grow older, these differences will tend to become less marked." 

36 



562 FUNDAMENTALS OF FRUIT PRODUCTION 

Rough lemon stock is said to produce tall upright trees of the varieties 
worked on it. 26 

Seasonal Changes. — In the orchard or vineyard, cultural practices 
have, in the majority of cases, no very obvious influence on the time of 
starting growth, but the effect on ripening and maturity is more marked. 
The classical experiment of introducing a vine or a branch of a tree into 
a warmed room during the winter, keeping its connection with the parent 
stock and observing it start growth while the remainder of the plant is still 
dormant, would lead to the inference that the cion is practically indepen- 
dent of the stock in the spring flush of growth. So it proves in most cases. 

End-season Effects. Ripening of Fruit. — Concerning effects at the 
other end of the growing season there is some conflict of evidence. It is 
rather well known that some of the annual species of Convolvulacese 
become perennial when grafted on perennial species. 37 Daniel reports 
that by grafting the annual parts of certain perennials on certain other 
perennial plants he has succeeded in prolonging the life of the cions. 49 
Conversely, in some instances, cions of perennials grafted on annual 
stocks have died at the usual time for the stocks, though Lindemuth 97 has 
shown a case where the plant lived longer. Such instances as these are 
more striking than those observed in fruit plants, where the possibility of 
change is necessarily more limited. It is sometimes claimed that grafting 
in itself hastens maturity in grapes by a few days. Cole 40 states that 
several growers in Victoria claim a few days earlier ripening in peaches 
worked on almond than on peach stock, while in France Sahut 130 claims 
that the Myrobolan plum induces earlier ripening in peaches than does 
almond stock. Sahut states also that cherries ripen earlier on Laurocera- 
sus than on ordinary cherry seedlings and the Reine Claude plum on 
Damas is said to be somewhat earlier than on St. Julien. Cole reports 
that heavy autumnal rains in Victoria are not so likely to induce second 
growth or fall blossoming in plums worked on Marianna roots as in those 
worked on Myrobolan and attributes this to the early dormancy of the 
former stock. 

In America topworked trees were more common formerly, propor- 
tionately at least, than they are now and discussions of mutual influences 
were correspondingly more frequent. These discussions show a sur- 
prising variety of experience and opinion, particularly in the effect of the 
stock on the time of ripening of fruit in the autumn. Diametrically 
opposite results apparently come from identical combinations of stock 
and cion. Hovey recounted extensive combinations of early pears on 
late and vice versa in Massachusetts, without any change from the usual 
season of ripening. There was, however, rather good evidence that 
plums on Myrobolan ripened earlier than on late plums. In apples, 
Shaw states that "particularly with Rhode Island Greening the season of 
ripening is influenced by the stock." 137 



THE RECIPROCAL INFLUENCES OF STOCK AND CI ON 



563 



The trifoliate stock is generally conceded to secure early ripening in 
oranges. Florida experience seems to indicate that oranges on rough lemon 
stock cannot be held on the trees as long as when grafted on sour orange. 147 

The grape, however, supplies the best examples of stock influence on 
fruit ripening. Wickson states that the Riparias Gloire and Grand Glabre 
induce ripening one to two weeks ahead of Rupestris St. George. Hed- 
rick found that many American grapes on Gloire and Clevener stocks 
consistently ripen their fruit ahead of the same varieties on their own 
roots. In the St. George there was less uniformity of effect; in fact this 
stock seemed to retard the ripening of some varieties. This difference of 
a few days is likely to assume considerable practical importance with 
late varieties in regions where autumnal frosts come early or where 
autumnal rains are frequent. 

Husmann 83 considers that the degree of congeniality between cion and 
stock influences the time of ripening. From this point of view it may be 
inferred that the same stock may have a retarding effect on one variety 
and hasten the ripening of another. Much conflicting evidence, in other 
fruits besides grapes, may be reconciled in this way. 

Table 2, including data taken more or less at random from Husmann 's 
figures, indicates that this possibility may be realized. Taking Lenoir as 
the standard, grapes on St. George have ripened, in one case 4 days ahead, in 
another case 9 days after, Lenoir. Dog Ridge has ripened fruit on its 
cion varieties 2 days ahead and 13 days after the same varieties on Lenoir. 



Table 2. — Ripening Dates op Grape Varieties on Different Stocks 

{After Husmann 83 ) 







Stock 




Variety 


Dog Ridge 


Lenoir 


Rupestris St. 
George 


Aramon 

Bastardo 

Beclan 

Bicane 

Blauer Portugieser 


Sept. 29 
Sept. 23 
Sept. 28 
Sept. 23 
Sept. 23 
Sept. 28 
Sept. 26 


Sept. 27 
Sept. 20 
Sept. 28 
Sept. 23 
Sept. 10 
Sept. 15 
Sept. 28 


Sept. 28 
Sept. 25 
Sept, 26 
Sept, 24 
Sept. 15 


Boal de Maderc 


Sept. 24 


Bolynino . . 


Sept. 24 







Data introduced later to show differences in the composition of fruit 
on several stocks may be anticipated here. Those differences that are 
found can be considered to represent such as might occur in separate 
specimens on the same tree or vine. Much of the available data is from 
European sources, or, if from America, it concerns such plants as are 



564 FUNDAMENTALS OF FRUIT PRODUCTION 

shown elsewhere to be rather sensitive to temperature conditions during 
the growing season. In other words, nearly all the available data con- 
cern plants or situations such that the difference between heat required 
and heat available is small. The grape in the northeastern states is 
near the limit of its summer heat requirements; the pear and the apple 
are not. 

The evident readiness of European authorities to recognize small 
differences in ripening according to the stocks used and the preponderance 
of American opinion — aside from a few instances — to the contrary can be 
reconciled if the climatic differences are considered. Just as a few days of 
unusual heat in the spring will force into simultaneous bloom varieties 
that blossom at different times in a cooler season, the greater heat at 
harvest in America probably obscures small differences that would be 
apparent in a cool region or in a cool season. 

End-season Effects. Maturity of Wood. — Evidence of the effect of the 
stock on the maturity of the wood, on the contrary, seems brought out 
more clearly in America than in Europe because of the different winter 
climates and the intimate relation of maturity to hardiness. There is, 
however, some mention of these effects in parts of France. Baco reports 
considerable difference in the time of ripening of the wood in grapes, 
stating: "In recapitulation, the grafted vines ripened their canes less 
than vines on their own roots. In this respect many grafts have appeared 
to us to be influenced by the stock about as they would be by nitrogen- 
ous fertilizers or by a mellow deep and fertile soil if one had not grafted 
them." 4 Since these differences have most intimate relation to hardiness, 
they are discussed under the effects of the stock on hardiness. 

The fall of leaves from a deciduous stock does not cause the fall of 
leaves on an evergreen cion. Though the trifoliate orange is deciduous, 
other varieties worked on it are not; though the quince is deciduous, a 
grafted loquat top is evergreen. This holds true in other cases. How- 
ever, despite this retention of foliage, it is probable that the deciduous 
stock has some effect tending toward a partial dormancy. Evidence of 
this lies in the smaller injury at a given temperature to orange on trifoliate 
than on evergreen stocks and in the possibility of transplanting the 
loquat on quince without "balling" of the roots, provided the leaves are 
stripped, though this cannot be done if it is on its own roots. 

Spring Effects. — Returning, for the sake of completeness, to the effect 
of stock on spring growth, the behavior of cherries on Chicksaw plum 
may be cited as typical. The stock starts much earlier and throws out 
leaves and shoots while the cherry grafts remain dormant until their 
customary season of growth." 69 However, Brown 29 recognizes a delay 
in blossoming of plums and almonds on certain varieties of plums. He 
states: "Blossoms appear on plums from 1 to 2 weeeks later than the 
almond. Where the plum stock has been tried the delay has been about 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 565 

one-half the difference between the two blooming periods." It seems 
quite possible that this difference can exist in one climate and not in 
another. A retarded entrance into the rest period in the autumn is 
shown elsewhere to delay the opening of peach blossoms in the spring. If 
the plum stock prolongs growth in the fall, it will evidently have a re- 
tarding effect on blossoming in the spring. However, the rest period is a 
retarding factor only in climates with mild winters and early springs and 
it is only in such climates that the retarding influence of plum stocks would 
become obvious. In the north the rest period ends before the dormant 
period and no retarding influence from the stock would be expected. 

Baco 2 recorded considerably more copious bleeding in Baroque and 
Tannat grapes grafted on various American and hybrid stocks than on 
their own roots. He also reported differences in the time of breaking of 
the buds; those on the own-rooted vines opened much more regularly and 
somewhat earlier than those on the grafted vines. As a rule the vines 
on hybrid stocks blossomed later and more irregularly. 3 

Here again, as in the ripening of fruits, it is in Europe and particularly 
with grapes that more attention is given to slight differences due to stocks 
and here again climatic factors explain the few differences observed. 

Several European commentators are inclined to emphasize the need 
of substantially the same seasons of growth inception in stock and cion 
to insure compatibility. Lindemuth states that his investigations have 
led him to the same conclusion in this respect as that of Lucas, to wit : a 
graft of an early starting kind on a late starting kind is never successful: 
" . . . late starting kinds grafted on early starting stocks, very fre- 
quently become sick, since they are not able to take up the quantity of 
sap which the early-starting seedling offers. Canker injuries at the point 
of grafting are very often the consequences of defective grafts of this 
kind. Less easily does the early starting cion become sick on late starting 
sorts. The more nearly equal in time and strength the growth of the 
cion and stock are, the better, according to the opinion of Dr. Lucas, is 
the success of the graft." 102 

An expression of the same influence in the apple in Brittany is fur- 
nished by Duplessix; 63 " ... if one inserts a cion of Doux Normandie 
[blossoming in June] on a stock from seed of Launette [blossoming late 
in April], the sap will ascend in the trunk 6 weeks before the graft is 
ready to receive it. The tree may die. If it lives the sap will accumulate 
in the swelling at the base of the graft and this swelling . . . can 
become in its turn a cause of death. ... If the reverse be tried, the 
cion of Launette will require sap when the Doux Normandie trunk is 
not ready to provide it and the cion of Launette will perish or it will grow 
slowly for want of feeding at a useful time. 

"... A stock starting earlier than the graft is preferable to one 
starting later." 



566 FUNDAMENTALS OF FRUIT PRODUCTION 

Though these two views differ in details, they agree in the general 
harmfulness of great differences in the starting season between stock and 
cion. The very fact that these differences can become harmful is evi- 
dence against any considerable modification of either stock or cion in 
season of growth inception. 

In brief, then, the influence of the stock on the season of the cion may 
be stated, for spring manifestations, in Knight's words: "The graft, or 
bud, whenever it has become firmly united to the stock, wholly regulates 
the season and temperature, in which the sap is to be put in motion, in 
perfect independence of the habits of the stock, whether these be late 
or early." Concerning the effects on autumnal processes, it may be said 
that some influences exist but may be obscured by the climate and that 
they are not necessarily parallel to the nature of the stock. 

Hardiness. — As to the effects of the stock on the hardiness of the cion 
there is considerable conflict of evidence, due in part, perhaps, to lack 
of precise definitions. It is frequently stated in European pomological 
literature that pears on quince stock are much freer from canker than on 
pear stock. Elsewhere in this work rather strong evidence is cited to 
show that the common frost canker of Europe is associated with lack of 
maturity. Evidence presented earlier in this section suggests that cer- 
tain stocks may affect the season of maturity of the tops. 

Hardiness has been shown to be involved to a great extent with water- 
retaining capacity which in turn appears to depend in no little degree on 
maturity. It may be affected by cultural practices and in some cases, 
apparently, by the stocks used. The stock may, to this extent,. be con- 
sidered to induce hardiness in the top. If, however, the conception of 
hardiness be that of a specific property which is present or absent there 
is no evidence that it is transmitted from stock to cion. It is conceivable 
that a stock may in itself be hardy but through the congeniality of the 
graft it may actually diminish the hardiness of the cion. 

Fruit growers of the upper Mississippi Valley have a well defined 
belief that such varieties as Jonathan and Grimes are rendered hardier 
by topworking on Haas, Oldenburg and similar hardy varieties. It 
seems plausible that with some varieties there is a certain increase in 
hardiness due to a slightly earlier maturity; more important, however, 
is the consideration that the cases under examination are not so much 
cases of increasing hardiness as they are of substituting a hardy variety 
in those parts of the tree that are particularly susceptible to winter injury. 
Even though the hardiness of the cion were not increased in the least, a 
tree of Jonathan topworked into Oldenburg framework could not help 
but be hardier, though only within limits. Macoun, 104 in Canada, top- 
working such varieties as Baldwin into hardy stocks, was unable to 
increase the hardiness sufficiently to stand a test winter. 

Hedrick 76 reports that Mahaleb stock makes hardier tops in cherries, 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 567 

both in nursery and in orchard, because of the earlier ripening of the wood. 
Prunus lusitanica is said to ripen its wood earlier on Prunus Padus stock 
than on its own roots and to withstand cold weather better, probably 
on that account. 44 Budd 31 reports the Jonathan apple ripening its 
terminal shoots better on Gros Pommier "than on its own roots" and 
states that "the hardiness of a variety is increased by the influence of a 
stock with a determinate habit of growth. ... In our own State 
[Iowa] we have evidence that by the selection of proper stock we can 
grow Jonathan or Dominie on low, wet soils where they would not reach 
bearing size, root-grafted . . . the main utility with us of top-working 
on such prepotent stocks as Gros Pomier, Duchess, Wealthy, Wolf River, 
etc., is in the way of fitting the less hardy scion for enduring the tempera- 
ture of our test winters." 

Experience with grafted grapes in regions where winter killing is 
important was more extensive in an earlier generation than in the present. 
The literature of the times shows a tendency to agreement in the increased 
hardiness of certain varieties such as Iona and Adirondac on hardy stocks 
such as Concord. Precise observations as to the reason for this were 
not common, but the suggestion was made that Iona roots were tender. 118 
The increased hardiness was secured, if this be true, by the substitution 
of a hardy variety in a tender part and not by changing the nature of the 
cion. Here again, roots inducing early maturity appear to increase 
hardiness. Nicholas Longworth, 79 after extensive trials, reported, 
"Foreign vines grafted on our natives are equally tender as on their own 
stock and are, with me, often killed down to the native stock." 

It is not, it should be noted, invariably the stocks inducing early 
maturity that are hardiest. St. George stocks, as reported by Hedrick, 
induced late growing in many cases; however, they suffered rather less 
from winter killing than the other stocks tested. Hedrick suggested that 
the deep rooting habit of this variety may be connected with its hardiness. 

Onderdonk 116 and Vosbury 147 reported that in the Gulf States the 
trifoliate orange increased the hardiness of the varieties worked upon it 
and attributed the hardiness to the deciduous habit of the trifoliate, 
inducing a degree of dormancy in the cion varieties and thereby making 
them more cold resistant. In the freeze of 1913 in California lemons 
worked on orange trunks proved more hardy than those on their own 
trunks, hardier not only in the orange trunks but in the lemon tops. It 
was suggested 152 that in some way the trunks of the trees modified the dor- 
mancy of the tops. This condition was more apparent in young trees 
than in those of bearing age. As in the Gulf States, trees on trifoliate 
were somewhat hardier than those on other stocks. In cases of severe 
injury, however, when the entire top has been killed, the trifoliate 
is unable to send up any sprouts and dies, though it has not itself suffered 
any direct injury from the cold weather. 



568 FUNDAMENTALS OF FRUIT PRODUCTION 

Disease Resistance. — Cole 40 recommends the "Kentish sucker as a 
cherry stock for fruit growers in Victoria because many varieties are 
less likely to gum when worked upon this stock than on Mazzard seed- 
lings." Presumably the gumming to which Cole refers is the physiologi- 
cal type. Barss, 19 in Oregon, recommends the genuine Mazzard stock 
as freer from bacterial gumming than miscellaneous seedlings from the 
ordinary sweet varieties. This, however, is another case of substitution 
in part of the tree rather than of change in the part grafted in, since to 
secure the greater freedom from the disease it is necessary to grow the 
tree two or three seasons in the nursery or the orchard and then graft 
it over in the limbs. 

Sometimes increased resistance to fungous diseases is claimed from 
top working, as in the gooseberry on Ribes aureum, but no evidence is 
available of any direct influence. In the case just cited any increased 
resistance is due probably to the changed habit of the plant, the increased 
height securing better aeration. 

In California the black walnut is used as a stock for the English 
walnut (Juglans regia), in large part because of its resistance to a soil 
fungus, the mushroom root rot (Armillaria mellea), to which the English 
walnut roots are very susceptible. This is, again, a case of substitution 
and not an influence of stock on cion. 

The claim is sometimes made that certain stocks make the top more 
or less resistant to insect or fungous attack. Since vigorously growing 
trees are more subject to aphis or to fire blight and perhaps less subject 
to certain cankers, it is quite conceivable that a stock affecting growth 
may indirectly have such an influence. The same effect, however, can 
be secured by cultural practice and no available evidence indicates 
any modification of a specific nature in the cion by the stock making it 
more or less liable to insect or fungus attack. 

Physiological Diseases. — Diseases of a mosaic nature are, of course, 
transmitted in either direction by grafting. Daniel 53 states that some 
cases of court noue in the grape can be traced to grafting and expresses 
the belief that it is due to "a kind of physiological trouble induced by 
osmotic changes caused by the union of plants of different chemical 
functional capacities." Daniel's statement that the characteristic 
shortened internode appears also on shoots from the stock suggests a 
condition similar to the transmission of pathological variegation rather 
than a specific change due to grafting. Daniel states that grafted beans 
grown in nutrient solution were free from chlorosis longer than check 
plants which had absorbed more of the solution. "Since the chlorosis 
could not be attributed," he states, "to anything but the presence of 
an excess of a salt (carbonate of lime, or another), it is necessary to 
admit that this salt has passed in less quantity because of the different 
osmosis and because of its utilization at the graft-union to neutralize the 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 569 

acidity of the wound surface. In a word, these results show very clearly 
that the graft, considered by itself, modifies the regimen of water and 
of soluble salts, that is to say, of the functional capacities of the grafted 
plants." 

In support of this view he cites Viala and Ravaz to the effect that the 
Herbemont grape was free from chlorosis on Clairette; likewise Merlot 
on Viala. It seems possible that these last instances may be due to a 
high degree of congeniality between the varieties mentioned. Blunno 25 
states that many resistant stocks are without chlorosis until they are 
grafted, but become so afterward, explaining this through the weakening 
of the plants by grafting. Susceptibility is greater, he reports, when the 
graft is not well healed and any weakening influence such as a fungus or 
insect pest, even on a resistant variety, favors infestation by phylloxera. 

Since John Lawrence, 93 in 1717, noted the transmission from the cion 
to the stock of variegation in leaves, this fact and its converse have been 
cited as standard evidence of the influence of stock on cion or of cion on 
stock or both. Numerous instances of such transmission are easily found, 
but have lost much of their significance through the view that in many 
cases variegation is a pathological condition and that grafting is in such a 
case also an inoculation. Variegation arising from other than patho- 
logical causes seems not to be transmitted from stock to cion or from cion 
to stock. 

Yield. — Some commentators are disposed to believe that grafting 
per se disposes the plant to fruitfulness. This is well expressed in this 
statement: "Seedling apples, especially those which are of a vigorous 
nature, run to wood and produce few fruits, or begin very late to produce 
them. Grafted apples, on the contrary, begin earlier to fruit." 62 . . . 
Undoubtedly early bearing is favored by grafts which have not united 
perfectly, just as it is by ringing or by any influence obstructing trans- 
location. Whether grafts which unite readily have the same effect is 
not so clear. Precocity of bearing is necessary to the success of any 
variety in cultivation; deficiency in this respect is the chief objection 
to the Northern Spy apple and the chief reason that it is now so little 
planted. Naturally, then, grafted trees of cultivated varieties tend to 
come into bearing early; otherwise the varieties would not be in culti- 
vation. Some varieties come into bearing at an earlier age than others, 
though all are grafted presumably on the same stocks. This time can 
be hastened or retarded by cultural means. Vigorous seedlings are 
late in bearing; so are vigorous grafted trees. There seems no clear 
evidence that grafting in itself, as commonly practiced in fruit trees, 
hastens the time of bearing. 

The influence of different stocks on the functioning of the cion is 
shown neatly by experiments such as those of Lindemuth 98 on potatoes. 
This investigator found that the potato on Datura, a vigorous growing 



570 FUNDAMENTALS OF FRUIT PRODUCTION 

stock, forms aerial stolons freely. The combination plant grows vigorously 
and manufactures much starch which cannot go into tuber formation as 
it would in an ordinary potato plant. It is, therefore, because of the 
vigor of the stock, utilized in the conversion of the potato stolons into 
leafy shoots. On a weakly growing stock, however, such as Capsicum 
annuum, starch accumulation exceeds utilization and tuber formation 
ensues from the buds which on Datura stocks give rise to shoots. 

Fruit-bud Formation. — Voechting 146 "has shown that buds which grew 
from the base of the inflorescence of a beet in the second year came out as 
leafy shoots supplied with large leaves, if they were grafted on a 1-year 
beet; on the contrary, they infloresced if they were placed on a stock 
already in its second year." 

Leclerc du Sablon 94 shows differences in total carbohydrates in 
the tops of Angouleme 2 years grafted on pear and on quince stocks. 
Except in May the carbohydrate content of the pear on quince is higher 
than that of the pear on pear. In view of the importance of carbohy- 
drate content to fruitfulness this difference seems of possible signifi- 
cance, though it is comparatively slight at the ordinary time of fruit 
bud formation. 

Table 3. — Total Carbohydrates in Tops of Angouleme Pears Grafted on Pear 

and on Quince 

(After Leclerc du Sablon 04 ) 

(Per cent, on dry weight basis) 

On Pear On Quince 

Jan. 19 23.7 25.9 

Feb. 26 21.7 25.4 

Mar. 28 24.3 27.9 

May 9 21.6 21.3 

June 17 22.2 22.6 

July 22 22.6 22.9 

Sept. 7 24.5 25.8 

Oct. 16 23.4 25.4 

Nov. 22 23.4 25.3 

Dec. 26 23.4 25.5 

Specific citations are hardly necessary to show the influence of 
certain stocks on fruit-bud formation. The dwarfing stocks, through 
limiting growth and therefore carbohydrate utilization, have a general 
tendency to permit sufficient carbohydrate accumulation for free forma- 
tion of fruit buds. European and Japanese chestnuts, for example, 
worked into chinquapin, bear in 1 or 2 years. 42 It should be remem- 
bered, however, that the total framework on which fruit buds can be 
formed is smaller and the total production of fruit buds on a given area 
of ground is not necessarily greater and may even be smaller, when 
dwarfing stocks are used. In some cases certain stocks not dwarfing 
in themselves make poor unions with cions set in them and exercise a 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 



571 



dwarfing effect. Some Wildgoose plums are said to be more fruitful 
on peach roots. 68 

These instances are introduced here, not as showing a general tend- 
ency toward any marked influence of stock on cion, but rather the 
dearth of more positive evidence. Considering the amount of top- 
working that has been done, little evidence of a change of practical im- 
portance has been accumulated. There has been a general tendency 
to assume that if there is any influence on the size of fruit the dwarfing 
stocks tend to produce larger fruit. Most of the instances just cited 
fail to bear out this idea. 

In Victoria Cole 40 reports that many varieties of plums which are 
shy bearers on Myrobalan stock are prolific on Marianna. "Although 
some varieties . . . somewhat overgrow this stock it is no great fault 
but an improvement — it influences the bearing qualities of varieties so 
inclined to overgrow. " 

In France some years ago, according to Pepin, 117 there was a dwarf- 
ing apple stock, neither Paradise nor Doucin, known as the Pommier 
hybride or batard; grafts on this grew vigorously but bore little fruit 
and that little was inferior. 

Bioletti, 23 reporting on the St. George grape stock, states: "In some 
cases the vines grow well but the crops are unsatisfactory. This has 

Table 4. — Product of Panariti Grapes on Different Stocks at Fresno, Cal. 

(After Husmann Si ) 



Stock 



Yield (in pounds 
per vine) 



1917 



1918 



Sugar content 
(Balling scale) 



1917 



1918 



• Acid as tartaric 

(grams per 100 

cubic centimeters) 



1917 



1918 



Adobe Giant 

Aramon X Rupestris Gan- 

zin No. 1 

Dog Ridge 

Lenoir 

Mourvedre X Rupestris 

No. 1202 

Riparia Gloire 

Riparia X Rupestris No. 

3309 

Rupestris St. George 

Salt Creek 

Solonis X Riparia No. 

1616 

Average 



7.5 

21.0 
3.0 
1.5 

8.0 
5.0 

17.0 
6.5 

8.0 

24.5 
10.2 



7.5 

11.0 
3.0 
2.0 

1.5 
2.0 

20.0 
2.0 
1.5 

19.0 

6.95 



30.5 

28.0 
26.5 
28.0 

23.5 
23.5 

28.5 
28.5 
28.0 

29.0 

27.4 



27.0 


0.9675 


26.0 


0.7650 


28.0 


0.8300 


26.0 


. 6450 


28.0 


0.8700 


30.0 


0.8850 


26.0 


0.8650 


26.0 


0.7800 


26.0 


0.7800 


26.0 


0.6900 


26.9 


0.80775 



0.8770 

0.8255 
0.8250 
0.7500 

0.7575 
0.9450 

0.8250 
0.8550 
0.8175 

0.8325 

0.8310 



572 FUNDAMENTALS OF FRUIT PRODUCTION 

been noted only in rich valley soil of the coast counties and only with 
certain varieties. A similar condition has often been noted in Europe, 
but it is usually easily overcome by longer pruning and diminishes with 
age. " 

Husmann 84 shows very striking differences in the product of the 
Panariti or currant grape on various stocks in California, as shown in 
Table 4. 

Rolfs 126 suggests a difference in the value of different stocks for the 
mango. The kumquat on sour orange roots grows a vigorous tree but 
it is practically barren. 

Fruit Setting. — A casual survey of European literature shows a con- 
siderable body of opinion to the effect that the setting of fruit is influenced 
sometimes by the stock on which the fruiting wood is worked. Par- 
ticularly does this appear in grapes. Ravaz is quoted to the effect that in 
sandy soils strong growing stocks fail to set fruit and for this reason many 
of the Riparia and Rupestris hybrids are not well suited to such soils. 145 
Baco 3 found the short and reflexed stamens characteristic of many hybrid 
stocks, but very rare in the pure Vinifera, produced in Baroque grafted on 
1202. These characters have been shown in the section on Fruit Setting 
to be associated with lack of viability in the pollen. Though it is not 
clear from Baco's account whether this condition was universal on this 
stock, he recorded it on other stocks also, including the Rupestris du Lot 
(St. George). Consequent upon this condition was a considerable 
amount of couture and of miller andage. Nevertheless, he recorded a 
general increase in production on these same stocks. 6 

Rupestris du Lot stock is reported to cause poor setting of fruit in 
many Victorian vineyards; 25 the vigorous growth of this same stock 
produces coulure in some varieties in California. 154 Odart, writing before 
the days of phylloxera in Europe, stated that the Raisin des Dames set 
fruit much better when grafted on the common white Muscat; 78 Bur- 
bidge 33 cites similar cases from the experience of forcing house grape 
growers. Baltet 14 states that the Cabernet grape when grafted is exempt 
from coulure beside own-rooted plants that are badly affected and quotes 
Hardy: "Graft the Chasselas Gros-Coulard, even on itself, and you will be 
resisting coulure." In Australia when the Kieffer pear is grown on wet 
soils better setting occurs if quince roots are used. 40 Sahut 130 states that 
Chionanthus virginica, grafted on ash, flowers abundantly but never 
fruits, while as a seedling it bears. 

Size of Fruit. — So many factors affect the size of fruit that it is difficult 
to find clear evidence of any considerable influence on size that can be 
attributed to the stock. Sometimes grape growers imagine an increase 
in the size of the individual berries when certain stocks are used. Bur- 
bidge, 34 for example, cited an instance in which the Gross Guillaume grape 
was considered to form larger berries on Muscat of Alexandria than 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 



573 



on Black Hamburg. Pepin 117 stated that certain almonds grafted on 
bitter almond or on St. Julien plum stocks bore smaller fruit. His 
statement of a stock which produced small fruit in the apple has been 
mentioned earlier. Daniel 55 found that tomato grafts on pimento pro- 
duced less fruit than on their own roots and that the fruit was generally 
smaller. The Golden Pippin in England when worked on free growing 
stock was said to be larger, mealy and poorer in keeping quality than 
on less vigorous stock. 106 In America some of the older generation of 
pear growers thought that small fruited varieties, such as Dana's Hovey, 
bore larger fruits when worked on vigorously growing stocks. The sand 
cherry has been said to produce larger fruits on Prunus americana than 
on its own roots. 67 Many California growers believe that peach roots 
induce larger fruit in both European and Japanese plums than plum or 
almond roots. 143 Hedrick, 75 however, reported no difference in numerous 
varieties of apples grown on Doucin, Paradise and standard stocks. 

Reference has been made to the greater growth of American grapes 
on certain stocks in an experimental planting in New York. 73 The same 
investigation showed much greater productivity in the grafted vines. 
Typical comparisons are shown in Table 5, condensed from Hedrick's 
results. Summarizing, on an acre-yield basis, the results for all varieties, 
including many not listed in the table just given, the yields by stocks for 
that year were, in tons per acre: on own roots, 4.39; on St. George, 
5.36; on Gloire, 5.32 and on Clevener, 5.62. Averages for 3 years were in 
the same order of magnitude. 

Table 5. — Average Yield per Vine of Own Root and Grafted Grape Varieties, 

1911 

(After Hedrick 73 ) 



Variety 


Own roots, 
pounds 


St. George, 
pounds 


Gloire, 
pounds 


Clevener, 
pounds 


Campbell 

Concord 

Vergennes 

Herbert 


16.00 
16.20 
17.36 
12.21 
15.17 
20.51 
15.37 
12.75 
14.43 
10.37 


23.69 
16.93 
22.13 
11.89 
16.42 
22.55 
12.95 
24.25 
15.56 
16.47 


20.41 
16 . 95 
24.52 
14.95 
17.68 
24.57 
16.41 
14.25 
13.06 
15.95 


18.35 
21.17 


Iona 




Niagara 


21.79 


Catawba 


21.94 


Delaware 


17.75 


Brighton 

Worden 


17.40 
15.71 



"The crop on the grafted vines was increased," Hedrick states, 
"through the setting of more bunches and the growth of larger bunches 
and berries. The increase in the number of bunches was easily deter- 



574 FUNDAMENTALS OF FRUIT PRODUCTION 

mined by actual count but for the statement regarding size we have only 
the fact that the proportion of unmarketable grapes was greater on the 
ungrafted than on the topworked vines. The greater fertility of the 
varieties on other than their own roots cannot be ascribed to larger vines. 
No data are available as to size of vines but judging by the eye alone the 
grafted vines do not make as much wood as do the varieties on their own 
roots." 

It should be stated that there is by no means a unanimity of opinion 
as to the effect of dwarfing stocks on the size of the individual fruit, even 
in Europe. 

Quality. — Practically all the older authorities were agreed that in 
some cases the stock influences the quality of the fruit borne by the cion; 
as to the extent of this influence there was more diversity of opinion. 

Downing, 60 writing in 1845, stated: "A slight effect is sometimes produced 
by the stock on the quality of the fruit. A few sorts of pear are superior in 
flavour but many are also inferiour, when grafted on the Quince, while they are 
more gritty on the thorn. The Green Gage, a plum of great delicacy of flavour 
varies considerably upon different stocks; and Apples raised on the crab, and 
Pears on the Mountain Ash, are said to keep longer than when grown on their 
own roots." 

Barry 17 spoke of the Beurre Diel pear as, "Sometimes gritty at the core on 
pear stock; invariably first rate on the quince." Again, of the Glout Morceau: 
"like the Duchesse d'Angouleme, Louise Bonne and some others, it is decidedly 
superior on the quince." 18 

Lindley" wrote: "It is not merely upon the productiveness or vigour of the 
scion that the stock exercises an influence; its effects have been found to extend 
to the quality of the fruit. This may be conceived to happen in two ways — 
either by the ascending sap carrying up with it into the scion a part of the secre- 
tions of the stock, or by the difference induced in the general health of a scion by 
the manner in which the flow of ascending and descending sap is promoted or 
retarded by the stock. In the Pear, the fruit becomes higher coloured and smaller 
on the Quince stock than on the wild Pear, still more so on the Medlar. . . . 
Mr. Knight mentions such differences in the quality of his Peaches. . . . Since 
the quality of fruit is thus affected by the stock, it seems allowable to infer that 
the goodness of cultivated fruits is deteriorated by their being uniformly worked 
upon stocks whose fruit is worthless; for example, the Almond or the austere 
Plum can only injure the Peaches they are made to bear, the Crab the Apple, 
and so on." Lindley cites with apparent approval numerous other instances 
of the sort. 

A generation later the grape growers of France were forced by the 
ravages of the phylloxera to confront this question in connection with the 
grafting of their Vinifera varieties on American vines whose fruit was, 
at the best, of indifferent quality. Much misgiving was felt lest the 
quality of the wines made from the new combination plants should be 
inferior to that of the older vines on their own roots. This great experi- 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 575 

ment, one of the greatest pomological experiments the world has seen, 
has failed to show any consistent deterioration in the quality of the prod- 
uct that could be attributed to the use of American stocks. In fact, at 
times wine from grafted vines has brought higher prices than that from 
the same varieties on their own roots. 15 

Sahut cites among instances where the quality is not injured by the stock, 
Vinifera grapes on American stocks, cherry on Mahaleb, almond on bitter almond, 
apricot on the common plum. In some cases, he states, more, larger and better 
fruits are secured by particular stocks, as in pears on the quince, apples on the 
Paradise, peach on the almond. The loquat on hawthorn, he states, is more 
perfumed and less acid than on its own or on quince roots, while of pears on haw- 
thorn some retain and some lose their quality. 

Some years ago California citrus growers hesitated to use sour orange 
stock through fear of spoiling the quality of their fruit, but extensive 
tests have shown no differences induced by either sour or sweet stock. 110 

Swingle 140 reports that the Satsuma orange on sweet orange stock 
bears fruit that is coarse, dry and insipid, as well as being later in ripening 
than on trifoliate stock, while on the latter the fruit is much improved in 
quality. Elsewhere the incompatibility between this orange and all 
stocks except trifoliate is discussed. 

In Pomaceous Fruits. — Riviere and Bailhache 122 present 3 years' 
average analyses of Triomphe de Jodoigne pears from trees of equal age, 
standing side by side, one on quince, the other on pear roots. The 
fruits on the standard tree averaged 280 grams in weight, those on the 
dwarf, 406 grams; total sugars per liter of juice: in the standard, 93.4 
grams, in the dwarf, 102.3 grams. The investigators calculate that a 
crop of 300 fruits would produce on the standard tree 7 kilograms of 
sugar and on the dwarf, 11. Two years' investigations on Doyenne 
d'hiver showed: On quince stocks, average weight of fruit, 435 grams, 
sugar percentage in juice, 11.59; on standard, average weight of fruit, 
230 grams, sugar percentage in juice, 9.04. 

Commenting on some experimental tests of dwarf apples in New 
York, Hedrick 75 states: "It is a common claim that dwarf apple trees 
produce larger, handsomer and better flavored fruits than standard trees. 
There is little in these three orchards to substantiate these claims. There 
are differences between trees on the three stocks but they are as often as 
not in favor of standards as of dwarfs." 

In Stone Fruits. — For the stone fruits Knight 90 may be quoted: 
"But I have subsequently planted two trees (of Moorpark apricot) 
growing upon plum stocks, and two upon apricot stocks, upon the same 
aspects, and in a similar soil, giving those upon the plum stocks the advan- 
tage of some superiority in age, and I have found the produce of the 
apricot stocks to be in every respect greatly the best. It is much more 



576 



FUNDAMENTALS OF FRUIT PRODUCTION 



succulent and melting, and differs so widely from the fruit of the other trees 
that I have heard many gardeners, who were not acquainted with the 
circumstances under which the fruit was produced, contend against the 
identity of the variety. The buds were, however, taken from the same 
tree. 



"I have also some reasons for believing that the quality of the fruit 
of the peach tree is, in some cases at least, much deteriorated by the oper- 
ation of the plum stock." 

In Grapes. — Curtel 47 reported a difference in must from Pinot grapes 
on their own roots and on Riparia roots. More careful studies in 1903 
are recorded in Table 6. In his discussion Curtel stated that there were 
differences according to the variety and the stock and that since the 
amount of organic nitrogen was thought to explain the observed differ- 
ences in susceptibility to wild yeasts the matter might assume considerable 
practical importance. 

Table 6. — Analyses of Juice Extracted from Grapes 
(After Curtel") 
(Parts in 1000) 



Pinot 

on 
Riparia 



Pinot 

on 

own roots 



Gamay 

on 
Solonis 



Gamay 

on 

own roots 



Dextrose 

Levulose 

Total acidity 

Bitartrate of potassium 

Phosphoric acid 

Organic nitrogen 

Ash 

Tannin 

Coloring matter 



87.30 
102.05 
9.20 
8.47 
0.46 
4.02 
5.15 
1.05 
100.00 



81.07 
98.05 
8.54 
8.51 
0.61 
3.17 
5.45 
1.85 
126.00 



153 . 50 

10.43 

9.41 



1.04 
100.00 



158 . 70 

8.60 
10.43 



1.10 
106.00 



Bioletti compares grapes grown on certain stocks: 22 "The quality 
of the grapes was in nearly all cases, where a comparison was possible, 
better on Riparia stock than on St. George. The grapes were larger and 
sweeter. The higher sugar content was, moreover, usually accom- 
panied by higher acidity, showing that the grapes were better developed." 
Quantitative data are shown in Table 7. 

Husmann 83 uses sugar and acid determinations of grapes as a test of 
the congeniality of the graft. Extensive determinations were made to 
test the effects of various stocks on the quality of the fruit. "These 
tests," Husmann states, "have yielded very interesting and suggestive 



THE RECIPROCAL INFLUENCES OF STOCK AND CI ON 



577 



Table 7. — Comparison of Composition of Grapes on Riparia and on St. George 

(After Bioletti 22 ) 









Stock 






Variety 


Riparia Gloire 


Riparia Grande 
Glabre 


St. George 




Sugar 


Acid 


Sugar 


Acid 


Sugar 


Acid 


Valdepenas 


27.5 


0.65 






23.5 


0.56 


Zinfandel 


26.5 


0.92 






24.0 


0.85 


Gros Mansene 


24.1 


1.20 


26.7 


1.12 






Fresa 


25.6 


0.92 


24.0 


0.83 






Vernaccia 


27.5 


0.84 


27.6 


0.92 


24.2 


0.61 


Marsanne 


23.3 


0.50 


25.0 


0.67 


21.6 


0.62 


Chardonay 


25.0 


0.60 


22.8 


0.87 






Sultana 


24.0 


0.75 






24.7 


0.75 


Cornichon 






20.3 


0.77 


18.4 


0.65 


Mean 


25.4 


0.80 


24.4 


0.86 


22.7 


0.67 



data which, when contrasted with the growth ratings of the same vines 
based on observations and measurements of growth during the same 
growing seasons, indicate that there is a close correspondence between 
these important chemical constituents of the fruit and the congeniality 
of graft and stock as determined by observation of growth. Similar rat- 
ings of the growth of a variety grafted on various stocks are found to be 
accompanied by fairly definite percentages of sugar and acid. Under 
like conditions of growth the sweetness and acidity of the fruit, as well as 
its time of ripening, are evidently materially influenced by the congeni- 
ality of the graft and stock." 

This is of considerable importance. It indicates that the congeniality 
of the graft is influential rather than the stock and that the same stock 
may with one variety increase the sugar content and with another 
decrease it. 

Qualitative Differences and Quantitative Variations. — Since com- 
position, ripening and keeping quality of fruits are more or less related, 
an effect produced on one of these implies an effect on the others. It 
was stated, many years ago, that there was a month's difference in the 
keeping quality of Hubbardston apples grown on Hightop Sweet and on 
Roxbury Russet in the same soil and with the same culture. Rhode 
Island Greening on Hightop Sweet was said to be only a fall variety. The 
crab stock of England made the Golden Pippin keep longer than did 
the free stock. Daniel, 54 who states that Labrusca stock has a rather 



578 FUNDAMENTALS OF FRUIT PRODUCTION 

unfavorable action on the table and wine qualities of certain white 
grapes, does not specify the nature of the action. 

These differences are quantitative rather than qualitative. No 
evidence is available showing a qualitative change in fruits, in the sense 
of an introduction or a manufacture of entirely different compounds, 
emanating from the stocks used. Furthermore, accepting all the cases 
alleged, there is still no clear evidence of any change beyond such differ- 
ences as could be effected by changes in maturity. A reference to Ravaz 
appears to show a possible relation of the stock to quality in fruit. It 
is stated 154 that, "to secure high gravity must in his opinion it is stocks 
with Riparia-like behavior which should be selected — one requires vines 
with slow and regular vegetation, the activity of which ceases early in 
the season. In a word, the vines should behave in as nearly as possible 
the same way as though they were growing on a dry hillside." 

Apparently, then, the nature of the fruit the stock bears is a matter 
of indifference; the two possibly important factors are (1) the vegetative 
habits of the stock, (2) the congeniality of stock and cion. In the light 
of present knowledge of the formation and ripening of fruit, it would be 
difficult to arrive at any other conclusion. An apple is sweet or sour 
according as it contains more or less sugar; the acid content is fairly 
uniform. This is determined largely in the spur or the neighboring 
branch; the trunk or roots cannot have much effect on it. The roots 
may keep the tree growing late and so influence the ripening, but the 
quality of the fruit the stock bears cannot be expected to influence the 
top. A stock with good fruit but unsuitable vegetative habits might 
influence the cion to produce inferior fruit and vice versa; a stock of a 
sweet variety may make the fruit of a cion sweeter or more acid. 

Longevity. — It is the generally accepted view that processes greatly 
increasing fruitfulness tend to hasten the ultimate death of the plant. 
This opinion has ample corroboration in the dwarf apples and pears and 
in recent years has been a very real problem to grape growers. Blunno 25 
mentions some instances that have a bearing here. 

"The Riparias, which are considered excellent stocks for loose, rich, deep 
soils such as are found on river flats, have given some disappointment in a few 
places in Sicily and Algiers," he states. "For the first few years vines grafted 
on them are loaded with fruit, which over-production seems to exhaust the 
plant. . . . 

" Similarly the Riparia X Rupestris No. 3306, which is generally planted in 
practically the same classes of soil as the Riparias and the R X R No. 3309, in 
soils a little stiffer, have gradually given signs of exhaustion in various localities. 
. . . Wherever the Riparia and Riparia X Rupestris hybrids failed it was 
always noticed that the exhaustion followed several years of very heavy crops; 
those vignerons who managed, by a skilful pruning, to keep the vines from yield- 
ing so heavily, have these vines still in bearing." 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 579 

Sometimes grafting has opposite effects. Without specifying as to 
the effect on fruitfulness, Jost records that Pistacia vera (the pistachio 
nut) as a seedling lives at the most 150 years, on P. lentiscus only 40, while 
on P. terebenthinus it reaches 200 years. 

General Influence of Stock on Cion. — Such evidence as is available 
on the influence of stock on cion has been presented. This influence 
wherever it is positive, is, almost without exception, quantitative. There 
is no doubt of the influence of stock on vigor and form of growth; there 
seems little reason to doubt some influence of the stock on the termination 
of the growing season, which is, after all, only a phase of vigor. If, now, 
the effect of stock on vigor be accepted, all other influences of stock on 
cion can be explained through that one influence. None of these influ- 
ences differs from effects that might be secured from so manipulating 
cultural conditions as to modify vigor. Cultural conditions can be 
changed to induce early fruiting or late growth or earlier ripening or 
hardiness or disease resistance or increased fruit-bud formation or better 
setting of fruit or larger or better ripened fruits. Girdling the grape 
will increase the sugar content and size of the fruit. The dwarfed trees 
of China that bear inferior undeveloped fruit are on their own roots; 100 
the inferiority of the fruit is brought about by manipulation, not by any 
influence of stock on cion. 

The influence of the stock on cion is not to be minimized; much 
harm has come from ignoring it. Frequently it is of extreme importance. 
However, it is important to the cion only as its vigor is important to the 
cion and as the graft union is satisfactory; the cion, for adjustment to one 
locality or purpose, may require a vigorous stock; for adjustment to 
another locality or purpose it may require a less vigorous stock or one 
that thrives in a soil of peculiar character. Adjustment of stock to cion, 
then, should be made with these factors in mind. In addition, the choice 
of stock should, where choice is possible, be made with soil, pests and 
cultural practices in view; conversely these should be considered in their 
relation to the stock as well as to the top. 

INFLUENCE OF CION ON STOCK 

Instances of apparent influence of cion on stock are more striking in 
plants other than those grown for their fruit, possibly because the 
interest of the fruit grower is centered chiefly in the cion and minor influ- 
ences on the stock are less likely to attract attention. Furthermore, an 
influence of cion on stock might involve a reaction on the cion and so 
be attributed to the effect of stock on cion. However, a few cases, some 
undoubted and some less clearly defined, are available for consideration. 

Just as among the influences of the stock on the cion, the effect on 
vigor and form of the cion are the most obvious, possibly because most 



580 FUNDAMENTALS OF FRUIT PRODUCTION 

readily observed, so among the effects of the cion on the stock those on 
vigor and form of the stock are most conspicuous. 

Size and Number of Roots. — Daniel, 48 working with various Cruciferae, 
found that in some cases when the cion belonged to a species of greater 
height than that of the stock it accelerated the growth of the latter and 
that, when conditions were reversed, an inhibiting effect was exercised. 
Sahut 131 stated : "If the cion belongs to a more vigorous species or variety- 
it stimulates the vigor of the stock. The common hawthorn, grafted 
with hawthorn bearing double pink flowers, with Sorbier des oiseleurs, 
Azerolier d'ltalie and the common Robinia grafted with R. decaisneana, 
develops much more rapidly. It is the same with the majority of Euro- 
pean vines [grapes] when grafted on American York Madeira or Rupestris 
stocks which are less vigorous. If the cion is less vigorous it restrains 
the vegetation of the stock. The Dwarf peach of Orleans, grafted on 
peach or almond, and Chinese plums on Damascene or St. Julien [are 
examples]. It is the same with the majority of European grapes on 
Riparia or Jacquez." 

Instances drawn from American experience are not lacking. Swin- 
gle 140 states: "Although the Trifoliate is naturally a small tree and of slow 
growth, when used as a stock its growth is so stimulated that its diameter 
always continues greater than that of the scion. . . . This form of 
union wherein the stock slightly outgrows the scion has been noticed also 
in the case of the loquat grafted on the quince growing at Eustis, Fla. 
In this case, also, the variety so grafted began to bear when still very 
young and has borne abundant crops since." Bonns 26 confirms the 
large growth of the trifoliate stock, even while it is exercising a dwarfing 
effect on the lemon tops worked on it. 

Brown 28 states that the Myrobalan root system is larger than usual 
if it is worked with peach tops. 

Bioletti and dal Piaz 24 compare Zinfandel and Tokay grapes growing 
on Rupestris St. George stocks. Here the stocks are cuttings and there- 
fore even more comparable than most seedling stocks. The greater 
growth of the Zinfandel top is balanced by a corresponding development 
of the root system. 

Whether the cause be incompatibility, poor graft union or something 
else, there is apparently sufficient evidence to warrant the statement 
that in some cases the cion does influence the stock. Since pruning 
the top of any tree, regardless of the stock, tends to reduce the root 
system and since some dwarf trees are kept so only by heading back, 
the necessity for seeking a mysterious influence is not apparent. A 
top which will not grow vigorously may be expected to act on the stock 
as would a heavy pruning; a top which is able to supply the roots with 
abundant food may be expected to increase their growth. Nevertheless, 
caution should be exercised against ascribing too much to this effect. 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 581 

Some grape stocks cannot grow fast enough to supply some cions; the 
sand cherry cannot be developed by a vigorous top to the size necessary 
for the successful support of a rapidly growing plum. If the implied 
effect of stock on cion be admitted, limitation in that of cion on stock is 
obvious. 

Distribution and Character of Roots. — Possibly because the root 
systems of nursery plants come under observation much more than 
those of the same plants once they are set in orchard or vineyard, there 
is considerable evidence of an effect of cion on stock in young fruit plants. 
Nurserymen frequently identify certain pear or apple trees by their 
root systems, though all are on seedling stocks. Hovey, 106 however, 
himself a nurseryman, indicated that this could not be done in all cases; 
some strong growing varieties, he stated, would have strong, and weak 
growers such as Winter Nelis would have correspondingly weak, root 
systems. It is stated that the roots of trees grafted with Siberian Crab 
"generally run down more than those of other trees. " 106 

Murneek 112 states: "Upright growing varieties of apples of the 
Russian type, for instance, will form a correspondingly deep growing 
root system while those of the Winesap type will be flat and shallow. 
This can be extended even to particular varieties. The Red Astrachan, 
Oldenburg, Fameuse, for example, form each a characteristic root system 
of its own. In this connection, Shaw believes 'that the size or stoutness 
of the main branches is positively correlated with the size of the main 
roots and angle of the branch with the angle of the main roots and the 
axis of the tree. In many individual cases this correlation is obscure, 
yet careful observations with large numbers of trees will reveal it.' " 
Bailey 8 stated that Northern Spy and Whitney tops make the roots 
of the stock grow deeper than usual. 

Waugh, 148 discussing plum propagation, reported:". . . Stoddard 
tops seem to give some of the curved tap-root character of the Americanas 
to all the stocks on which they grow. . . . One interesting point was in 
the way in which Stoddard tops induced a conspicuous branching of the 
root system when worked on peach. With other varieties the peach 
gave almost always a clean, unbranched tap-root. The weak growth 
of Green Gage naturally served to induce only a weak growth in most 
of the stocks on which it was worked; while the rampant growth of 
Chabot had exactly the opposite effect. The strongly branching root 
systems found on Chabot trees were probably due in part to the energetic 
way in which the foliage acted during the growing season. Marianna 
stocks, which seemed to be uncongenial to Milton, giving only a poor 
union, made very little growth when grafted with Milton scions. No 
other case was observed in which Milton appeared to have any influence 
on its stock. Newman seemed to influence all stocks in the way of 
giving off more secondary roots. Nearly all stocks when grafted with 



582 FUNDAMENTALS OF FRUIT PRODUCTION 

Newman gave a strong, vigorous growth, considerably above the average, 
tending at the same time to produce more both of secondary roots and 
of fibers." In the following year he reported: "No case was observed 
this year in which the scion showed any marked effect on the stock." 149 

Baco 5 cites numerous grape stocks in which the roots grow more 
spreading when grafted with Baroque; among these are: Riparia 
Gloire, Rupestris du Lot and Riparia X Rupestris 3306. On the other 
hand, Chasselas X Berlandieri 41 B becomes deeper rooted when grafted 
with the same cion variety. This last stock, it is said, succeeds best in 
warm, dry seasons and the deeper penetration of the roots is held to be 
disadvantageous in many locations and seasons. 

Longevity, Growing Season and Hardiness. — Some rather spectacu- 
lar instances of modification in growing habits of stocks are reported. 

Lindemuth 98 grafted an Abutilon cion on the roots of an annual plant, Modiola 
caroliniana, and thereby kept the combination plant alive 3 years and 5 months. 
Althcea narbonnensis has tops which die to the ground every winter. Grafted 
with Abutilon Thompsoni, a plant of Althcea with no other top could not secure 
the proper materials for forming winter buds and died. Another specimen, 
similarly grafted, but sending out a sucker from the root, lived and kept the 
cion living over a year. Daniel 49 obtained similar results with Solarium 
pubigerum on Giant tobacco, which is an annual in Brittany. 

Sahut 131 cites numerous instances of evergreen cions, as Cratcegus glabra 
and Raphiolepis on the common quince, etc., succeeding on deciduous stocks. 
However, these cases lose some of their significance in the light of present knowl- 
edge of winter processes in deciduous plants. The same writer states that when 
the late opening St. Jean walnut is grafted on the common walnut the stock "is 
obliged to hold back a month or more. Deciduous cherries," he states, "on 
the Laurier-Amande (evergreen) make the stock rest almost absolutely. The 
varieties of grape which push out late, Carignane, for example, grafted on Riparia 
or other American species which start sensibly earlier, hold the stock back. The 
European early starting grapes, as Aramon, when on late American stocks, as 
York Madeira, force the stock to earlier growth." 

Perhaps more definite information may be secured from certain 
instances where the cion appears to have an effect on hardiness. 
Since this is in many cases a matter of maturity the effects recorded may 
be considered equally as effects on maturity. 

Vard 144 in an extensive survey following the severe winter of 1890-1891 in 
France found that rose stocks which had supported cions of Tea and Bourbon 
roses had not only lost their cions but were themselves killed back to the ground. 
Unbudded stocks or those which had supported hardy varieties suffered little. 

Following the cold wnter of 1913 in California Webber and others found some 
apparent cases of "a definite influence of the tops upon the stocks. In one case," 
they report, "in the spring of 1912 a nursery of sour seedlings was budded to 
Eureka lemons. Many of these buds did not take, so that during the freeze of 



THE RECIPROCAL INFLUENCES OF STOCK AND CION 583 

January, 1913, there were in this nursery, at the same elevation and under the 
same conditions, yearling lemon tops on sour stock (buds had been inserted 
several inches above the ground) alongside of sour seedlings. While a slight 
injury to the foliage was the only harm experienced by the latter, the lemon 
tops were killed, and the frozen wood extended 3 to 4 inches down on the sour 
stock. Similar conditions were found on pomelo stock while the pomelo seedlings 
were scarcely touched." 152 

Other Influences. — Sahut states that quince roots topworked to pear 
are more particular in their soil requirements than those not worked over; 
they require a more fertile soil. However, as he indicates, the general 
rule is to the contrary; otherwise the selection of lime resistant, drought 
resistant and moisture resistant stocks would be to no point. The cion 
itself does not render the stock subject to phylloxera or immune to 
woolly aphis, though a lack of congeniality may induce weakness and 
hence a lack of recuperative power. The transmission from cion to stock 
of variegation has been discussed previously; it cannot be regarded as an 
instance of true influence exerted on the stock by the cion. 

In General. — Just as in the case of stock on cion, in considering the 
influence of cion on stock it is not necessary, so far as fruit plants are 
concerned, to predicate any direct effect other than on vigor. Every 
other influence that has been established or attributed can be explained 
as exercised indirectly through vigor and can be placedoon a quantitative 
basis. This action on vigor may be direct when the two parts to the 
graft are congenial and make a good union, or it may be indirect when 
there is apparent uncongeniality and the union is poor. Qualitative 
influences, such as the passage of alkaloids across the graft, or the barring 
of inulin by the graft, are not necessary to explain any observed phe- 
nomena resulting from grafting in fruit plants. 



CHAPTER XXXII 

THE ROOT SYSTEMS OF FRUIT PLANTS 

The choice of stocks for the various fruits, where any considerable 
latitude is possible, is frequently rather complex. First, two economic 
interests are concerned, the grower's and the nurseryman's; second, 
several natural factors, the congeniality of the union involved, the 
relation of the stock to the soil, to the climate and to the variety. Rarely 
is it possible to secure a stock that meets all requirements in all situations; 
the result is generally a compromise. 

CONFLICTING INTERESTS OF NURSERYMAN AND FRUIT GROWER 

The nursery business, like most businesses, is competitive. The 
individual nurseryman is, therefore, sometimes compelled to adopt 
certain alternative choices which may not be to the best interest of the 
grower or, ultimately, of the nursery business itself. The responsibility 
for this situation rests not with the nurseryman alone, for as long as 
growers will buy cheap trees, ignoring their real value for the conditions 
under which they are to be grown, all nurseries are more or less forced 
to offer cheap trees and often find difficulty in selling better. The 
nurseryman's immediate interest, then, rests in securing stock that 
is cheap, that makes a good union, with a high percentage of successful 
grafts, and that makes a marketable tree quickly. 

The plums, with the multiplicity of species cultivated for fruit and of 
species available for stocks, serve as an excellent illustration of con- 
flicting interests and factors. Some years ago it became evident that for 
successful plum culture in the north central states a very hardy stock 
was necessary. The Americana stocks met the growers' requirements 
very weld in nearly all respects. However, seed for growing the stocks 
in large quantities was not readily available. The Marianna stock, 
rooting readily from cuttings in the south, was much cheaper. Trees 
on Marianna roots could be produced at little expense and were sold at a 
price which virtually precluded competition from the better suited, but 
higher priced, trees on Americana roots. Want of discrimination on the 
part of buyers of nursery stock made this situation possible. Waugh 
furnishes another illustration. The St. Julien plum, he states, is the 
best stock for Domestica plums, making "a better, stronger, longer-lived 
tree than Myrobolan." He proceeds to quote a nurseryman's letter, 
in part, as follows: "St. Julien stocks are much preferred by the orchard- 

584 



THE ROOT SYSTEMS OF FRUIT PLANTS 585 

ists in this locality, because trees certainly do better in every way on that 
stock. They sprout less from the root, are longer-lived, and generally 
more vigorous than when on Myrobolan stocks. We occasionally plant 
some St. Julien seedlings, but do not make a practice of it, because 
in the first place St. Julien seedlings cost more than double the price of 
Myrobolans, and they are not as thrifty the first year they are trans- 
planted. They also are attacked by a fungus which causes them to lose 
their leaves early in the summer, thus preventing the budding of the 
stocks altogether, or a partial failure in the buds when this leaf fungus is 
not corrected. Of course, when taken in time we can in a large measure 
prevent this falling of the leaves by spraying with Bordeaux mixture, but 
taking all things into consideration, it is quite a bit more expensive to 
raise plums on St. Julien stock, and we find that we cannot get any more 
for them in the open market, so that we have become discouraged growing 
stocks on the St. Julien root." Hedrick quotes J. W. Kerr of Maryland 
to the effect that though for that section he prefers the peach as a stock 
for the Domestica plums, there are many varieties of this species that 
will not form a good union with the peach and in these cases he is forced 
to use Marianna or Myrobolan stock. 

Growers of Vinifera grapes have found that no one stock is suitable 
to all conditions. Cuttings of a given species may not root freely and 
it is eliminated from the list of available stocks, no matter how resistant 
it may be to phylloxera or how desirable in other respects. Another 
species or variety may not give a large percentage of successes in bench 
grafting and the establishment of a vineyard on this stock becomes a 
matter of more labor and greater expense. 

Dawson 58 gives the scarcity of seed as the chief reason against the 
employment of Pyrus betulcefolia which he states would be a very satisfac- 
tory stock for pears on dry soil. 

The Mazzard stock for cherries is preferred by growers in some sec- 
tions, but nurserymen have rather forced the use of Mahaleb. The 
Mazzard has several features which make it rather unsatisfactory for the 
nurseryman; one of these is its sensitiveness to weather conditions in 
the nursery row so that though buds may take readily one season the 
following year may give entirely unsatisfactory results, or the budding 
season may close abruptly before the work is complete. 66 

Enough evidence has been introduced to show that the best stock for 
the nurseryman, under existing circumstances, is not always best for the 
grower. The responsibility, however, rests with the grower. When he 
is so convinced of the superiority of a given stock that he is willing to pay 
the price for it, the nurseryman will produce trees on that stock. Until 
the grower realizes that the best stock in the orchard may not be the 
best stock in the nursery or vice versa the nurseryman can do only as he 
has been doing. 



586 FUNDAMENTALS OF FRUIT PRODUCTION 

ADAPTATION OF STOCKS TO PARTICULAR CONDITIONS 

Further, it must be remembered that a plant that is valuable to the 
grower in one location may prove otherwise in another. Climatic condi- 
tions may simplify the choice for a certain grower by eliminating all 
but the most hardy stocks, but they may complicate matters for the 
nurseryman who is selling to a wide territory. 

Adaptation to Soil Temperatures. — A grower ordering stock from a 
nursery in a milder climate should consider that he may be getting trees 
with stocks not adapted to his conditions. A northern grower, for exam- 
ple, securing plum trees from the south, would do well to make sure that 
they are not on peach or Marianna roots, though some of the leading 
nurseries no longer use these stocks. The southern grower may be more 
interested in securing a stock that will not sucker or in extreme cases, as 
cited by the Howards, 80 he may even require a stock that is able to endure 
high soil temperature. These investigators found that in Baluchistan 
the peach and plum stocks commonly used in Great Britian would not 
succeed, but by using stocks which they considered better adapted to hot, 
dry soils, such as Marianna, Myrobolan and Mahaleb, they secured much 
better results. 

Adaptation to Soil Texture and Composition. — Prune trees in the Paci- 
fic northwest have been planted in many cases without much regard to the 
stock on which they were worked. In numerous instances prunes with 
peach roots have been planted in rather heavy, poorly drained land in 
which the planting of peach trees would not be considered. 

French horticulturists had not solved the problem presented by phyl- 
loxera when they had isolated certain varieties of American grapes that 
were resistant to this pest, that lent themselves to making good cuttings 
and satisfactory graft unions with the Vinifera cions. Many of the 
French vineyard soils are strongly calcareous; in these soils only compara- 
tively few of the American vines flourish. Hence, ability to withstand 
calcareous soils must be considered in any choice of stocks for rather wide 
use in France. When California vineyards were invaded by phylloxera 
the stocks tried and approved in France were naturally given early 
consideration. However, lime tolerance is not so important in California 
since comparatively little vineyard soil is calcareous; of much greater 
importance, in some localities in this state, is ability to withstand drought, 
in others ability to flourish in soils with a high water table for part of the 
year. Rupestris St. George (du Lot), because of its deep roots, with- 
stands drought better but suffers severely when the water table stands 
near the surface for long; the shallow rooted Riparia Gloire and certain 
Berlandieri hybrids meet requirements here. Most Vinifera-American 
hybrids adapt themselves to these conditions. The Muscadine grapes 
also are adapted to moist soils and hot climates. 113 In California, as in 



THE ROOT SYSTEMS OF FRUIT PLANTS 587 

France, ignorance of local conditions and of the stocks suited to them may 
indeed lead to utter failure. 

Other plants than the grape prove refractory on calcareous soils in 
France and in many cases recourse to a lime resistant stock has proved 
successful. Dental 59 furnishes an instance in the Australian Acacia 
dealbata which grows freely in calcareous soils on A . floribunda though on 
its own roots it will not grow in such soils. A similar expedient is neces- 
sary for the growth of certain pines in these soils. Some Australian exper- 
ience seems to indicate that sour orange is the best stock for orange and 
lemon in sections where the irrigation water is likely to contain alkali 
in considerable quantities. 146 California experience indicates that lemon 
is unusually susceptible to alkali. 87 On the other hand, lemon roots are 
stated to be the best foragers in poor soils in this section. Prunus davi- 
diana is now under trial in California as an almond stock; the particular 
quality commending it is its ability to grow in more alkaline soils than 
other commonly used almond stocks. 142 Two successive plantings of 
peaches in one California orchard were killed by alkali; following this 
peaches on Davidiana roots have proved successful in the same soil. 143 
Cock 38 states that the trifoliate orange, though it is too dwarfing in its 
effects to be a commercial success, may be used to advantage in very wet 
soils. In the Gulf States the trifoliate succeeds in rich, moist soils and is 
unsuited to light, dry soil. 147 Pomelo in California appears to suffer 
most from drought. 26 Sahut 130 states that in wet soils the peach and 
apricot grow better on plum roots than on their own or on almond roots 
and that the cherry on Mahaleb grows in poor soils where it would not 
grow on its own roots. 

The degree of refinement to which adaptation of stocks can be carried is shown 
by Bioletti's tentative recommendations of stocks for Vinifera grapes in Cali- 
fornia : 22 

"The Rupestris St. George has given its best results in the hot, dry interior on 
deep soils. . . . 

"For a great majority of our soils and varieties the two Riparia X Rupestris 
hybrids 3306 and 3309 promise to be superior in every way to the St. George. 
The former for the moister soils and the latter for the drier. . . . 

"For the wettest locations in which vines are planted — in places where the 
water stands for many weeks during the winter, or where the bottom water rises 
too near the surface during the summer — the most promising stock is Solonis X 
Riparia 1616. 

"For moist, rich, deep, well-drained soils, especially in the coast counties and 
on northerly slopes, the St. George is utterly unsuited. The crops on this stock, 
in such locations, are apt to be small, and the sugar content of the grapes defec- 
tive. In these locations the Riparia Gloire is much to be preferred, and will 
undoubtedly give larger crops of better ripened grapes. 

"None of the above stocks give good results, as a rule, in very compact soils. 



588 FUNDAMENTALS OF FRUIT PRODUCTION 

For such soils the most promising varieties are 106 8 in the drier and Aramon X 
Rupestris No. 1 or 202 4 in the wetter locations. In dry, shallow soils 420A 
and 157 11 give promise of being excellent stocks." 

Some stocks show such catholicity in taste that it is safe to grow trees 
on them for planting in all locations that are at all suited. The Cali- 
fornia black walnut, for example, adapts itself to so many soils that it is 
almost universally used in California as stock for the English (or Persian) 
walnut, though its resistance to root rot (Armillaria mellea) is also an 
important factor. 

Sorauer 138 quotes Lieb to the effect that Pyrus malus prunifolia 
major and P. m. baccata cerasiformis have been found valuable as stocks 
for apple in very exposed or dry positions. 

Immunity or Resistance to Soil Parasites. — Adaptation to soil must 
be paralleled at times by adjustment to diseases. The Damson plum 
seems rather resistant to crown gall and in special cases might be given 
preference for this reason. Shaw has found that cion-rooted apple trees 
show crown gall in different forms according to variety. "Thus," he 
states, "the Jewett apple shows usually if not always the hard form of the 
gall, the Red Astrachan the simple form of the hairy root and the Olden- 
burg the woolly knot form with many soft fleshy root growths. Other 
varieties show the brown root form and still others often the aerial 
form. . . . 

"Some varieties on their own roots seem to be largely if not entirely 
immune to this disease. If this proves to be really the case, here may lie 
the solution of the problem of the prevention of crown gall. . . . Prob- 
ably the economic advantage would warrant the extra effort necessary to 
propagate such trees, only under conditions where the crown gall was 
especially troublesome. 

"There are other root diseases which are injurious, especially through 
the southern part of the apple belt, that might possibly be avoided in a 
similar fashion." 135 

The pear affords an interesting example. The so-called Japanese 
pear (Pyrus serotina) is more resistant to blight than the French stock, but 
seems rather susceptible to mushroom root rot and is sensitive to soil 
moisture. Choice between the two may at times involve nice discrimi- 
nation. In some soils the lemon suffers from root rot to such an extent 
that other stocks are substituted. In Florida the sweet orange roots 
formerly used as stocks were so badly attacked by root rot that this 
stock has been superseded. Similar susceptibility is found in California. 
In regions subject to pear blight the displacement of French seedling 
pear stock by other stocks, such as Pyrus serotina, P. ussuriensis and 
P. calleryana, that are resistant or immune can be forecasted, except as 
other troubles may develop. 



THE ROOT SYSTEMS OF FRUIT PLANTS 589 

PROPAGATION BY CUTTINGS 

Under this head are considered the various forms of cuttings, layers, 
stools and the like which depend on the formation of roots from the wood 
of the variety to be cultivated, without the intervention of grafting or Duel- 
ing. All plants thus propagated are on their own roots. The list of fruit 
plants so propagated commonly includes the fig, olive, grape, currant, 
gooseberry, mulberry, filbert and pomegranate from hardwood cuttings; 
the various dwarfing apple stocks and quince from mound layers or stools ; 
the strawberry by rooted "runners;" the black raspberry, loganberry and 
dewberry by rooted tips of canes, the red raspberry and blackberry by 
suckers; the cranberry and blueberry by hard or soft wood cuttings or 
by "tubering" or "stumping" as the case may be. If pomological 
literature be searched at all carefully there appear some rather sur- 
prising additions to the list of plants that can be propagated by cuttings, 
particularly by hardwood cuttings, including frequently the citrus fruits, 
plums, pears and apples. 

"Some of the plums grow well from cuttings. This is especially true of 
Marianna, and millions of Marianna cuttings are made every year in this coun- 
try, mostly for stocks. . . . The St. Julien plum grows fairly well from cut- 
tings, and nearly all the Myrobolan varieties may be propagated this way. Some 
of the Japanese varieties, especially Satsuma, have been grown from cuttings 
in the southern states. Practically, however, propagation by cuttings is con- 
fined to the Marianna." 150 

That the apple may be propagated by cuttings is indicated by quota- 
tions from Knight, though possibly he is describing what is now known to 
be a rather common pathological condition in the apple. 

"There are several varieties of apple tree, the trunks and branches of whioh 
are almost covered with rough excrescences, formed by congeries of points which 
would have become roots under favorable circumstances; and such varieties are 
always very readily propagated by cuttings." 88 The Paradise and Doucin 
stocks root more or less readily from cuttings. 

Darwin 56 cites Tennent as saying, "in the Botanic Gardens of Ceylon the 
apple tree sends out numerous underground runners which continually rise into 
small stems, and form a growth around the parent tree." 

Ribston Pippin is said in England to grow readily from cuttings. 

Again quoting Knight: "Peach and Nectarine trees, particularly 
of those varieties which have been recently obtained from seed, may be 
propagated readily by layers, either of the summer or older wood; and 
even from cuttings, without artificial heat; for such strike root freely." 91 

Advantages and Disadvantages. — Propagation by cuttings may or 
may not be advantageous; there is nothing in the process itself that makes 
it one or the other. When it is readily accomplished it is obviously the 
cheapest process, but the plant may do better on some other roots than its 



590 FUNDAMENTALS OF FRUIT PRODUCTION 

own. The lemon, for example, is reported in Australia 40 as inferior on 
its own roots, being more susceptible to unfavorable soil moisture con- 
ditions. The Vinifera grapes root readily from cuttings but the roots so 
formed are subject to phylloxera infestation; recourse is therefore made to 
grafting these grapes on resistant stocks which in turn are grown from 
cuttings. The Oldenburg apple on its own roots appears decidedly 
inferior, 134 though Mcintosh and Stayman make notably fine growth on 
their own roots. Sometimes when it would be desirable to have trees on 
their roots their failure to root readily from cuttings makes the process im- 
practicable. Many of the apples and plums that are extremely resistant 
to cold winter weather form, if set deeply, roots from the cion that are 
much hardier than those of the stocks commonly supplied. A method of 
ready propagation by cuttings in such cases would be of great advantage. 
To meet this difficulty special methods have been devised; these are dis- 
cussed presently. To take advantage of the relative immunity of North- 
ern Spy roots to the woolly aphis, Australian growers take considerable 
pains to develop these roots, either by layering, stooling or grafting with a 
"starter," and upon the Spy stock work the variety they wish to grow. 
In some cases, then, fruit plants which grow readily from cuttings are 
grafted on other stocks at greater expense; in other cases, plants which do 
not form their own roots readily are induced to do so, though such plants 
are more expensive. 

Objection is sometimes made to plants propagated by cuttings as 
compared with those developed on seedlings, because of certain supposed 
shortcomings. They are occasionally said to be shallow rooted; Hatton, 70 
however, states, regarding dwarf apple stocks: "We have found it just 
as possible to raise stocks of deep anchorage by layers and other vegeta- 
tive methods as it is easy to find shallow-rooted ones in any collection of 
free stocks raised from pips." This supposed shallowness of the root 
system was turned to account by the early Spanish settlers of Louisiana, 
who propagated the peach by layering to suit it to alluvial lands where the 
water table is high. 119 Cock, 39 writing on citrus fruits in Victoria, states 
that layers and cuttings are always weak and more liable to disease than 
seedlings. Macdonald, 103 also in Victoria, writing of the olive, states: 
"It is possible that, in poor soils or trying situations, the seedling may be 
the more thrifty and long-lived tree, but experience in this country has not 
gone to prove that this is the case. Many of the oldest trees in Australia 
were raised from truncheons and are still doing well. However, their age 
is comparative youth in the life of the olive tree, and perhaps it is as well 
to accept the opinion of continental writers on the greater longevity of 
seedling trees until there is greater evidence at. hand to the contrary." 
In New South Wales seedling plums are considered to make better 
root systems than cuttings. 1 Grapes, gooseberries and currants have 
passed through many generations of cuttings, without perceptible 



THE ROOT SYSTEMS OF FRUIT PLANTS 591 

diminution in vigor. The process, therefore, apparently is not per se 
devitalizing. It has, moreover, certain marked advantages, one of 
which is uniformity of the roots. 

This uniformity in the roots frequently is of considerable importance. 
The constant tendency to variation in seedlings is not confined to quality, 
color and size of the fruit but extends to every character of the plant. 
They may vary in vigor of growth as much as in the color of the fruit; 
the quality of fruit varies no more than the stature ; the depth of rooting, 
resistance to cold, to drought, to moisture, to alkali, all are variable 
characteristics. Hatton 70 states: "Free stock is a comprehensive term, 
meaning no more than seedlings which include dwarf stocks both fibrous 
and stump-rooted, as well as vigorous ones resulting from a well-balanced 
root system." The seedling root, then, is in a measure an unknown 
quantity. The tree planted in the orchard is standardized above ground, 
uncertain below ground. The stock for any individual tree may be more 
vigorous or more hardy or more resistant than the average; it is just as 
likely to be less so. In France the prospective grape grower whose soil is 
strong in lime knows that certain stocks do not thrive on those soils; he is 
able to pick a lime-enduring stock, for grape root stocks have been stand- 
ardized through growth from cuttings. If, however, he has a rocky, 
thin soil in a hot, dry exposure, he can select another stock, known to be 
the best for such locations. Were he to rely on seedlings he would be 
indulging in a lottery whose results could be told only after a year or more. 
To replace those which failed he would use more unknown quantities. 

Grapes in Particular. — Varietal differences in the character of root 
systems produced from cuttings are recognized in grapes. Bioletti and 
dal Piaz 24 explain the susceptibility of Riparia and the immunity of 
Rupestris stocks to drought by the shallow roots of the former and 
the deeply penetrating roots of the latter. In poorly drained soils and 
in soils with the water table high for any length of time, these same 
peculiarities tend to reverse the order of suitability. Hedrick sug- 
gests that the small amount of winter killing of grapes on Rupestris 
St. George stock as compared with that on other stocks in an experimental 
vineyard in New York may have been due to its deep rooting habit. 73 
The advantage of having stocks of known performance is obvious. 

Apples and Pears in Particular. — Fortunately apple and pear stocks 
are fairly adaptable. They seem so, certainly- — perhaps because there 
is no standard with which to compare them. However, every careful 
grower recognizes that some of his trees consistently bear more or less 
than others. This raggedness may be attributed to minor variations 
in soil and doubtless correctly so in many cases; it is sometimes attributed 
to bud variation, though the work of Crandall 45 and of Gardner 65 suggests 
the doubtful importance of this source of variation. The unevenness 
in a seedling orchard strongly suggests that were the tops all removed 



592 FUNDAMENTALS OF FRUIT PRODUCTION 

and grafts of one variety inserted on the roots the resulting trees would 
show considerable differences in vigor and productiveness. Mention 
is made elsewhere of results in Missouri showing considerable variation 
in seedling apples. 

Hatton 70 states, in the course of a comparison of Paradise, free and crab 
stocks: "We are faced, then, with two converging series quite arbitrarily divided, 
the one ranging from dwarfness to vigour and the other from vigour to dwarf- 
ness; the only real distinction being that the Paradise series has been raised 
vegetatively, and any particular member of the series can be reproduced by that 
method again and again, whilst the free series has been raised from seed, and as 
long as this method is employed infinite variety and inequality will continue, 
except in rare cases. 

"It is often argued that 'true crabs' are less variable than 'ordinary free 
stocks ' but I cannot learn what the trade distinction stands for. If free stocks 
are the chance children of cider fruits, crabs (commercial not botanical) are the 
chance progeny of wildings; but every district has many, many so-called crabs 
varying in vigour and character. I have seen them strong and clean; dwarfing 
and root knotted, whilst the types of fruit are various. I do not pretend to 
assert that free stocks from particular sources may not be more even than from 
other sources. That simply depends on the chance crosses, on the varieties 
mixed or cross pollinated, which in some cases may be more advantageous than 
in others; but I do say that stocks raised from pips will always be variable, and 
therefore incompletely satisfactory, except for the purpose of raising new types 
of stock for subsequent vegetative propagation, if we find degeneration or im- 
perfection in the existing types." 

Examination of an orchard, injured here and there by root killing, 
forces belief in the variation shown by the seedling roots and an apprecia- 
tion of the desirability of a stock that is uniformly hardy. If a vigorous, 
hardy, resistant stock could be isolated and propagated, much of the 
unevenness in yield and uncertainty in hardiness would be eliminated. 

Furthermore, the importance to the experimenter of having each tree 
on its own roots should be emphasized. The lack of uniformity in 
yields of trees in the same plot in fertilizer, cultural or pruning experi- 
ments has done much to invalidate results and more definite conclusions 
might well be expected if the root systems as well as the tops of the trees 
were identical. 

Vegetative propagation of apple stocks seems not only of probable 
value but worthy of study as a real possibility. Hatton 70 in a paper 
of great importance reports that in the investigations of Paradise apple 
stock at East Mailing one type was isolated which is free growing, not 
in the least dwarfing in its effects; this stock is propagated readily by 
vegetative methods. Further study of this type and search for others 
like it seem of great importance. The great amount of variation found 
by Hatton gives promise of isolating stocks which will show particular 



THE ROOT SYSTEMS OF FRUIT PLANTS 593 

adaptabilities to different conditions in a manner comparable to those 
now catalogued for grapes and of making possible much finer fitting 
of trees to environment. 

Propagating Apples and Pears by Layerage and Hardwood Cuttings. — 
Investigation of propagation of apples and pears by hardwood cuttings 
seems of possible value as well. These cuttings root readily in the 
tropics and in some of the southern states, such as Florida, Mississippi 
and Texas, and could perhaps be rooted elsewhere if proper soil tempera- 
tures were provided. Kieffer and LeConte among pears and Northern 
Spy among apples seem to root especially well, though this ability 
is possessed by other varieties. Similar cases have been reported in 
England. 

Warcollier in France is reported to have had mediocre results with 
cuttings of 30 to 50 centimeters of the previous season, well ripened; 
success was possible only with soft wooded varieties. Others in France 
reported very satisfactory results using branches of 3 or 4 years' growth, 
with side growths removed, plunged into the soil to a depth of 10 to 25 
centimeters. Varieties of moderate or feeble vigor, particularly one 
known as "Petit doux, " gave the best results. 64 

The propagation of the Northern Spy stocks used for all apples in Victoria 
is chiefly from layers and stools. The parent Spy stocks are planted 2 feet apart 
in rows 4 or 5 feet distant in June (autumn in Australia). The processes followed 
are described by Cole: 40 "In August cut back to within an inch of the ground 
level, so as to get a supply of buds to or below the soil to push out. The 
following August cut back to two buds any weak or light growth, pegging down 
the stronger parallel with the row or other planted stocks. The buds upon the 
pegged-down growths, being now brought into a vertical position, will send up a 
sufficient supply of shoots for working upon sound lines. About November, 
mould them up lightly by removing some of the higher soil from the middle of 
the rows. During the following winter remove soil about the layers and cut 
away any light shoots that may have rooted hardening back others close to 
the main layer. 

"The propagator should not be too eager in removing rooted shoots from the 
main layers until after the fourth season, but will be repaid by cutting hard back, 
forming good, well-rooted crowns for future use. From now out the operator 
will require to use his own judgment regarding the growths he cuts hard back and 
those he leaves for pegging down after removing any that may be rooted. In 
the winter mould up after cutting away any rooted stocks and the pegging down 
is finished, and again in November or December. Deep or over moulding should 
be avoided. 

"Stooling. — This method is somewhat similar to that of layering, but instead 
of pegging down the unrooted shoots they are cut hard back each year, so as to 
encourage as many as possible to show out. The second season from planting, 
and after the shoots have been cut back to within an inch or so of the stool, mould 
lightly, and again in November or December. If the shoots do not root, this 

38 



594 FUNDAMENTALS OF FRUIT PRODUCTION 

moulding will cause them to become bleached close to the crown of the stool. 
Upon being hardened back, shoots that give the best results will be formed. 
When removing rooted shoots in the winter, leave any that are very small for 
the following year; also any that are weak and spindly. . . . 

"The cooler and moister districts are the best adapted for the raising of Spy 
stocks by these two methods (layering and stooling), as the rooting of the shoots 
is controlled by even moisture during late summer and early autumn. From 
healthy, old, and well established stools, and those putting up medium and not 
over-strong shoots, the best results are obtained. The writer advises that layer- 
ing and stooling should be worked conjointly." 

The use of Northern Spy stock is mentioned by Wickson 153 in California. 
Paul C. Stark, however, states that Northern Spy has not proved satisfactory 
in the central states, as a stock, forming knots on the roots and rooting with 
some difficulty. 

In the northern central states where seedling roots have proved 
tender in the colder winters recourse has long been made to an indirect 
method of securing trees on their own roots. Long cions are whip grafted 
on small pieces of seedling roots and planted deep. Roots are formed 
more or less freely from the underground portion of the cion; since the 
varieties grown are necessarily hardy the roots seem to share in this 
hardiness and have proved actually hardier than the average seedling 
roots. In a short time these cion roots generally outgrow the seedling 
starter which becomes much reduced in proportion and plays an insig- 
nificant part in the mature tree. 

Varietal Differences and Contributing Factors. — Varieties differ in the 
readiness with which they emit roots in this way. Shaw 136 found that 
some varieties root readily, others only in very niggardly fashion; 
Baldwin, for example, showing 32 per cent., Ben Davis 51, Sweet Bough 
98, Delicious 22, Mcintosh 74, Jonathan 11, Grimes 41, Gravenstein 55, 
Northern Spy 58, Oldenburg 25, Tolman 3, Winesap 34, Wolf River 71, 
Yellow Bellflower 3, Yellow Transparent 26. He found also that the 
same variety performs differently from year to year, possibly from 
internal conditions, possibly from external. Stark reports that Delicious 
forms cion roots very readily and the roots are aphis resistant. Moore 111 
reports on similar work in Wisconsin. Of the varieties tested Livland 
Raspberry, Hyslop, McMahon, Pewaukee and Transcendent showed cion 
roots on 50 per cent, of the trees studied, in the third year. Cion roots 
are formed more readily in moist soil and, because of this, Moore con- 
cludes that grafts planted deep form roots more readily. Table 8, 
reproduced from Moore's report, shows the difference in cion root forma- 
tion in moist and in dry soil. 

Recent investigations in Iowa show that the formation of cion roots 
is much accelerated by winding the point of grafting tightly with a 
copper wire. 85 



THE ROOT SYSTEMS OF FRUIT PLANTS 



595 



Table 8. — Cion Roots Produced in Apple under Different Soil Moisture 
Conditions (After Moore 111 ) 





Trees observed 


Cion-rooted 


Strong cion-rooted 


Variety 


Moist 


Dry 


Moist, 
per cent. 


Dry, 
per cent. 


Moist, 
per cent. 


Dry, 
per cent. 


Peerless 

Northwestern 

Mcintosh 

Hyslop 

McMahon 


263 

142 

94 

40 

31 


311 
328 
110 
98 
103 


42.6 

63.4 

56.4 

100.0 

87.1 


31.4 
24.1 
29.1 
50.0 
32.0 


6.1 
18.3 
21.3 

100.0 
58.0 


5.8 

2.7 

1.8 

23.5 

10.7 



Maynard 109 mentions the use of short pieces of apple roots as nurse 
grafts for refractory quince cuttings. "The apple root," he states, 
"supplies moisture and a little food material until roots are formed on 
the cion, when it fails to grow more, and we have the quince on its own 
root." 

Another method of propagating trees on their own roots is the plant- 
ing of own rooted trees secured as just described and taking cuttings 
from the roots they form. This depends on the formation of adven- 
titious buds on the roots which some species and some varieties accom- 
plish readily while others apparently do not. 

Finally should be mentioned propagation of fruit trees, especially 
some of the plums and some varieties of apple, from sprouts arising on 
the roots. This method is perhaps more common in some sections of 
Europe than in the United States, partly because the varieties grown lend 
themselves to this treatment and partly because of the very positive, if 
somewhat exaggerated, prejudice in the United States against root 
stocks which sprout freely. 



SOURCES OF NURSERY STOCK 

With certain reservations it may be said that the proximity of the 
source of nursery stock is unimportant. If the stock is healthy, well 
developed and well matured, it will grow. Some of the ornamentals, 
grown from seed, tend to mature earlier if from northern seed than if from 
southern and there may be temporarily a somewhat readier response to 
climatic changes in vegetatively propagated plants from one section than 
from another but, if there is, it quickly disappears and there is little or no 
evidence that it is of any practical importance. 

It should, however, be realized that different stocks are used in grow- 
ing certain fruits by nurseries in different parts of the country and that 
this may be of extreme importance. The northern plum grower, for 



596 FUNDAMENTALS OF FRUIT PRODUCTION 

example, is more likely to get hardy plum roots from a nursery near home 
than he is from a nursery whose chief clientage is in a section with milder 
winters. 

For fall planting, northern growers will be more likely to get well 
ripened trees from northern sources where the trees naturally mature 
earlier. That this may assume importance is shown in the section on 
Temperature Relations. 

Withal the mere mailing of an order to a local nursery is not always a 
guarantee that the stock sent to fill the order is of local origin. Many 
nurseries buy much of their stock from distant points. However, if the 
stock is good and, in cases where a difference in roots is important, if the 
roots are of the right kind, the grower need not concern himself greatly 
about its origin. 

GRADES OF NURSERY STOCK 

Fruit trees are offered for sale by nurseries in several grades, which 
are based on size as measured by either height or diameter or both. Since 
the largest trees cost the most, the question whether there is any ultimate 
advantage in them is of practical importance. 

The very fact of the grading shows the difference between individuals. 
If this is a temporary matter, due to better immediate environment of 
one tree in the nursery row there will be no final difference in the growth 
and performance of these trees. If, however, the variation be an expres- 
sion of inherent differences, the planting of lower grade stock may have 
serious consequences. 

It is shown elsewhere in this section that bud mutations in the decidu- 
ous fruits are uncommon; hence, uniformity in the tops may be presumed. 
If there be a fundamental difference between the large tree and the small 
tree in the nursery the cause must lie in the stock. Most of the stocks 
used are seedlings and therefore more variable than the vegetatively 
propagated stocks, some kinds more than others. Some of this variation 
is undoubtedly temporary, but there are good reasons for thinking some 
of it is more deeply seated. 

Webber 151 reports investigations with citrus fruits that bring out these 
inherent differences in seedling stocks very strikingly. 

He summarizes his investigations in part as follows: 

"Nursery trees even when grown from selected buds taken from selected 
trees differ greatly in size when they reach transplanting age. Commonly the 
large trees are sold first and the small trees later when they reach the required 
size. 

"Large, medium and small nursery trees of Washington navel and Valencia 
oranges and Marsh grapefruit grown in comparative tests show that after 2\i 
years in the orchard the large trees remain large, the intermediate trees remain 



THE ROOT SYSTEMS OF FRUIT PLANTS 597 

intermediate and the small remain small. The evidence indicates that this 
condition is inherent in the trees and that in planting orchards only the large 
nursery trees should be used. 

"An examination of sweet and sour orange seedling stock, such as is used for 
budding, showed the presence of many widely different types. Some of these 
types were propagated and the trees at the end of the 4H years still show the same 
marked difference. Some are fully five times as large as others. Yet all such 
types are used as stocks. 

"Budding on seedling stocks of different types and unknown character of 
growth is believed to be largely responsible for the different sizes of budded 
trees developed in the nursery and also for many of the irregularities in size and 
fruitfulness of orchard trees." 

These differences probably hold for the apple. A seedling apple 
orchard seven years planted, at the Missouri Station, contains trees rang- 
ing in circumference from one inch to sixteen. It is not likely that if 
these seedling roots had been topworked to the same variety they would 
all have made equally good trees. From all appearances, they have 
maintained or increased — but not changed — their relative differences 
in size; the trees that are largest have made good growth each year, 
while those that are now inferior appear to have been inferior continuously. 

It should, however, be recalled that there are cases of a delayed effect 
in dwarfing. Plums worked on sand cherry frequently make vigorous 
growth in the first year, greater in fact than on other stocks which ulti- 
mately grow the larger trees. 

Gravenstein, on the Paradise apple in Germany is said to grow very 
vigorously at first, but to grow very little after bearing. 115 Chester 
Pearmain and other varieties behave similarly. 95 Like effects have been 
recorded with Castanea vulgaris grafted on Quercus sessiliflora in an attempt 
to grow chestnut in soils strong in lime; growth was very vigorous the 
first year, but few grafts lived till the third year. Even shorter was the 
success of Vinifera grapes on Cissus orientalis Lamarck. 127 Hatton 70 
may be quoted on this point: "It is often denied that this inequality in 
the stocks shows itself in the worked trees. Although it is true that a 
strong-growing variety, such as Bramley's Seedling, may largely obliterate 
this inequality in the maiden, differences again become apparent in the 
second and third years." To this extent, then, the grower buying 2-year 
old graded stocks of some trees may perhaps be a little surer of having 
runts weeded out. At present, however, the extent to which this delayed 
effect is operative in common fruits cannot be stated. 

Briefly, in buying nursery stock, the grower who gets trees of good 
size for their age, other things equal, is more nearly sure of getting trees 
that will do well in his orchard. Buying the smaller grades he is buying 
uncertain plants. They may be stunted only and may ultimately 
make good trees. They may, however, be composed of runts which are 



598 FUNDAMENTALS OF FRUIT PRODUCTION 

inherently incapable of being anything else. In practice the inferior 
grades probably contain some stunted and some "runt" trees. The only 
sure way of differentiating between them is the test of time which is 
likely to prove more costly to the grower than the difference in price. 
The inferior grades, therefore, should be regarded with suspicion. 

On the other hand, the extremely large tree is open to objections, seri- 
ous in some cases. If the tree is large only because it is older, only be- 
cause it has — as often happens — stood in the nursery an extra year or two, 
it carries no guarantee of inherent good growth; on the contrary, the 
presumption is against it. It may be only an older runt. 

Gardeners know well that the smaller the plant the less disturbance 
it suffers in transplanting and the more readily it reestablishes itself. A 
large proportion of the root system of the larger trees is cut off in 
digging. Data gathered in California show that the largest trees made 
the smallest percentage diameter increase during the first year in the 
orchard, indicating a slowness in adjusting themselves to the new loca- 
tion. 77 Furthermore, trees of unduly large size, produced sometimes by 
over irrigation or heavy fertilization, are more liable to winter injury when 
planted in the autumn. 

Other objections to the larger trees are voiced by Hendrickson : 77 
"Branches are often produced the first year in the nursery row. If 
these branches could be utilized they would be a distinct advantage but 
they are often broken or injured in the process of packing and must be 
cut off when the tree is planted. In other cases the branching does not 
begin near the bottom of the tree or the bottom branches have been 
shaded out, and hence it is difficult to secure a low-headed tree by using 
the branches produced in the nursery. Furthermore, the buds on the 
lower portion are far apart and the tree has a tendency to grow from the 
top buds. . . . 

"The small 1-year old tree as a rule, depending on the kind, produces 
few or no side branches. Consequently the buds, instead of growing into 
branches in the nursery, remain dormant until the following year. They 
are also less liable to injury in packing. Consequently the small tree 
within a few weeks after the beginning of the growing season is covered 
from top to bottom with leaves and small branches. The growth is 
generally more evenly distributed among the several growing points, 
than in the case of the overgrown tree." 

Withal, "large" and "small" sizes, or even grades based on definite 
measurements, are relative only. Different nursery fields, or the same 
fields in different years, produce trees varying considerably in size. 
Varieties differ more or less in their characteristic growths. Conse- 
quently even among trees of the same age any grading must be on a rela- 
tive basis; a certain caliper measurement may denote small trees in one 
case and medium sized trees in another. 



THE ROOT SYSTEMS OF FRUIT PLANTS 599 

Definite, though not invariable, objections have been shown to both 
extreme grades in nursery stock, on the one hand practical and on the 
other hand primarily theoretical but none the less real. The logical 
consequence is the approval of the medium grades. Experience usually 
justifies this course. 

Selection of Seedling Stocks.— For good or evil, seedling stocks will 
continue in use, for some fruits, indefinitely. It is likely, however, that 
at no distant time the sources of seedling stock will receive closer scrutiny 
than has been given. Indeed a rough selection has been exercised for 
many years in some cases. The so-called Vermont crab stock for apples, 
in reality grown from cider mill pomace and tracing ultimately in many 
cases to seedling apples, sometimes has been preferred to crab stock. 
Feral peach stock from Tennessee has been used to a considerable extent. 

Gradually, however, imported French seedlings have been used 
increasingly for apple stocks, because they were cheaper than native 
grown stock. With the rise of canneries, peach stones and cherry pits 
have been available at little cost to growers of nursery stocks and have 
been widely used. 

The variation in seedlings has been mentioned. It is probable, 
however, that investigation will show certain varieties to produce 
larger proportions of good seedlings than others. Commercial varieties 
of fruit are not grown for the value of the seedling stocks they produce. 
Doubtless some of them will prove of value for this purpose; others will 
not. 

Roeding 125 says: "For several years I have been carrying on experiments 
with different varieties [of peaches] todetermine their value from a standpoint 
of growth and general freedom from crown gall, and taking it all in all, the Salway 
comes first, and the trees produced from Lovell and Muir seed next. Within the 
last few years I have been carrying on experiments with Tennessee natural 
pits and am already convinced of their value as to the vigor of growth. If the 
root system is found to be healthy and of a fibrous character, this stock will be 
given the preference." 

Apple seedlings from different parentage will probably, in some cases, 
show differences worthy of consideration. Data from an orchard of 
seedlings of known parentage at the Missouri Experiment Station 27 
show a marked tendency to inferior growth in all seedlings of Ralls 
(Geniton) parentage. Careful study doubtless would show certain 
varieties to be admirable parents for nursery stock, while others would 
turn out to be parents of an unduly large number of runts, sources of loss 
both to nurseryman and to grower. 

The desirability of care in the selection of the source of seedling stocks 
has received attention in Europe. 



600 FUNDAMENTALS OF FRUIT PRODUCTION 

Duplessix, 61 writing on apple growing in Brittany, states: "The choice of 
apple trees furnishing seeds for sowing is very important, for the tree coming 
from the seed will generally have the principal characters of that tree which 
supplied the seed. But there are numerous varieties whose wood has a slow, 
twisting growth, without vigor, and these varieties are not suitable for generating 
good stocks, which ought to be straight and of a vigorous and rapid growth. 
Other varieties, as most of the Reinettes and Calvilles, are very subject to canker; 

" It is necessary then to extract the seeds from fruits from trees whose wood is 
healthy and of a very vigorous growth. Right here is a difficulty for cultivators, 
for the wood varieties generally used by nurserymen, such as the Frequin de 
Chartres, Noire de Vitry, Genereuse de Vitry, Maman Lily, yield few fruits or 
fruits of second quality and, for this reason, are almost unknown in our orchards." 

The same writer carries the matter of selection still further and 
advocates growing stock from seed of trees corresponding in season of 
growth inception with those whose grafts they are destined to bear. 

Grafted or Budded Trees. — Certain fruits such as cherries and peaches 
are propagated customarily by budding and no question is raised as to the 
• value of trees produced in this manner. Some others, as the apple, are 
readily propagated either by budding or by grafting and the question of 
preference between trees grown by these methods has been raised fre- 
quently. There may be a difference in the adaptability to a given locality 
of budded or grafted trees, but it rests on a basis other than that usually 
discussed. 

Much of the alleged superiority of budded trees rests on the use of a 
whole root in budding while in bench grafting one root may be cut to 
serve three or four cions. It is argued that this cutting down of the root 
system produces a tree that is permanently inferior to the budded tree. 
Budding frequently produces a larger tree in a given time in the nursery 
than grafting, but there is no positive evidence of any permanent differ- 
ence in trees raised by the two methods and there is much negative evi- 
dence that points to the absence of any difference due to the process used 
per se or the amount of root used per se. 

The real difference between budded trees and grafted trees has been 
appreciated only in certain sections where the difference was brought 
out occasionally by the death of one class and the survival of the other. 
Trees grafted with long cions and short pieces of root and set deep in the 
nursery tend to throw out roots from the cion, while the seedling root 
becomes unimportant or dies, as explained elsewhere. Experience has 
indicated that cion roots arising from wood of varieties that are hardy are 
themselves more uniformly hardy than the roots on which they are 
grafted. Such trees are therefore better adapted to localities where root 
killing is likely. It is regrettable that in recent years so many budded 
trees have been set in northern fruit growing sections where root grafted 
cion rooted trees provide an insurance well worth consideration. 



THE ROOT SYSTEMS OF FRUIT PLANTS 601 

Cion rooted trees may prove superior in other localities because 
of their persistence or spread or depth or other qualities. If experience 
with grapes is a valid analogy, considerable difference between varieties 
is these qualities would appear upon investigation, some cion roots 
proving superior and other inferior. In the one case, then, root grafted 
trees would be superior, in the other, budded trees, since the seedling 
roots would average better than the cion roots. In sections with cold 
winters, particularly sections with scanty snowfall, root grafted trees 
should be used. 

Double Worked Trees. — There are several possible reasons for double 
working: (1) a lack of congeniality between stock and cion, (2) need of a 
trunk and scaffold limbs that are mechanically stronger, (3) the top may 
be subject to disease or winter injury that is more or less characteristic 
of the trunk. 

Certain varieties of the pear unite poorly with quince stock though 
they unite well with pear. Therefore, on the quince is worked a variety 
that does unite well and into this as a stock is budded the desired variety. 
Beurre Hardy is used by many nurserymen as the linking variety. 
Bailey 9 recommends Angouleme for the same purpose; Rivers, 121 in 
England, found a number of varieties useful, including Beurre d'Amanlis. 
Clairgeau and Seckel are among the varieties said to thrive better when 
double worked. In California double working is favored for Bartlett 
on quince roots. 113 

Burbidge 35 mentions another combination in double working: "In soils 
which do not suit the Quince, but in which the Pear luxuriates, this order may 
often be reversed by using some good-constituted Pear as the root stock on which 
to graft the Quince, which again in its turn is worked the following year with 
the kind of Pear desired to form a fruiting specimen." He also quotes Parkin- 
son (1629) for another interesting example: "Speaking of the red Nectarine, 
then the rarest and dearest of all fruit trees, he remarks : ' The other two sorts 
of red Nectarines must not be immediately grafted on the Plum stock, but upon 
a branch of an Apricock that hath been formerly grafted on a Plum stock.' " 

The apricot as described by Baltet 12 is adjusted to dry sites along 
the Mediterranean by almond roots. Since the grafts do not take well 
in direct contact, double working is invoked, using a vigorous peach as 
the connecting link. The same author states that the Damask plum is 
sometimes used in France as intermediary between the peach top and 
Myrobolan roots. 11 

Certain varieties of apples are notoriously subject to collar rot. 
To escape this difficulty they may be worked on another variety that 
is noted for its resistance. Grimes double worked on Delicious in the 
nursery is now available. Delicious is said to induce vigorous growth, 
transforming Bechtel Crab, for example, into a much more satisfactory 



602 FUNDAMENTALS OF FRUIT PRODUCTION 

tree than the ordinary seedling stocks develop. It is probable that more 
of this kind of double working will be employed in the future. 

Blight resistant kinds of pear are coming into use as stock on 
which the more susceptible but better flavored pears are worked. The 
"Japanese" pear has been used for this purpose, with results varying 
because several species have been imported under this name. Some 
are comparatively tender, others are uninjured by a temperature of 
-40°F. or even lower; some are comparatively susceptible to blight, others 
practically immune. Among the more promising of these stocks are Pyrus 
ussuriensis, P. ovoidea and P. cattery ana. 120 The first of these is extremely 
hardy; the last is comparatively hardy and is able to thrive in very wet 
soils. There is no doubt that working of dessert varieties in limbs of these 
trees will greatly decrease the labor and cost of fighting pear blight. 

Top working to insure hardiness in the trunk is discussed elsewhere. 
It may be mentioned here, however, that the use of Rome Beauty trunks 
for Gravenstein, the leading apple variety in the Sebastopol apple section 
of California, has prevented the "sour-sap," which has been exceedingly 
troublesome there. 143 

An interesting possibility in the future of fruit growing in America 
is top working for the development of a better framework. Increasing 
competition will ultimately tend toward the use of fruit of high quality. 
Heretofore, varieties with good quality in fruit but weak growing habits 
have been discarded; enhanced appreciation of quality is likely to force 
the fruit grower to use such varieties whether he likes the tree or not. 
With weak growing varieties he will likely resort to top working on frames 
formed by more sturdy varieties. For this reason it is interesting to 
note that in growing certain choice dessert varieties many European grow- 
ers have followed this practice for a long time. Certain plums, as Petit 
Mirabelle, which are weak growers, are worked into a sturdy interme- 
diary such as Quetsche, Reine Claude de Bavay, St. Catherine, Krasensky 
or Andre Leroy. 13 In Algeria the Japanese plums grow better when 
top worked into peach limbs. The same process is followed with several 
pears. Growers of choice apples appear to resort to similar devices for 
Baltet lists numerous varieties as suitable intermediaries and states that 
nurserymen grow certain varieties especially for this purpose. 

According to Lindemuth double worked apple trees have been in 
great favor in Holland. A variety called "Sweet Pippin" is grafted 
into seedling stocks close to the ground and on this intermediary the 
fruiting variety is worked at the height of the head. The sole reason 
for this preference, it is said, is the thick trunk formed by the Sweet 
Pippin, obviating the necessity of supporting the young tree during 
its first few years by a stake. Since apple trees in northern Europe 
are grown commonly with much higher heads than in the United States 
this precise quality would be more important there. 



THE ROOT SYSTEMS OF FRUIT PLANTS 603 

Maynard 108 recommends working Bosc, a notoriously poor growing 
pear, into tops of strong growing varieties such as Ansault, Clapp or 
Flemish Beauty. In sections particularly subject to pear blight, how- 
ever, these particular frame stocks would not be advisable. Maynard 
stated in 1909 that Kieffer had been recommended for this purpose but 
had "not been successfully tried in the eastern states." 

It should be recorded, perhaps, that double working was advocated 
many years ago, for increasing the quantity and quality of fruit. Graft- 
ing in itself was supposed to have this effect and it was thought as voiced 
by Noisette, 162 that the more the operation was repated the greater 
would be the improvement. In more recent times, however, the tendency 
has been to use double working for more specific purposes, or not at all. 
Here again, as in so many cases, distinction must be made between the 
effects of the process itself and the effects of the material used in the 
process. 

PEDIGREED TREES 

Observation commonly shows much individual variation between 
the trees in an orchard that has been planted and tended with the purpose 
of providing conditions as uniform as possible. Furthermore, these 
differences extend to practically every feature of the tree growth and 
they are often extreme. Naturally this has suggested the possibility 
of perpetuating by vegetative propagation the favorable variations. 
There has been much discussion on this question and on the value of 
the so-called " pedigreed " trees that are grown from cions cut from indivi- 
duals of unusual excellence. In many cases very little actual evidence 
has been available and opinions have been based on an assumed analogy 
between a vegetatively propagated tree and a sexually reproduced animal 
or on theoretical considerations. 

Some Results with Citrus Fruits. — Shamel and some of his associates 
have clearly demonstrated that in a number of the varieties of citrus 
fruits there is a large amount of bud variation that is of real significance. 
A number of intra-variety strains have been isolated, propagated and 
have "bred true," if such an expression can be used for the vegetative 
propagation employed in the citrus fruits. 

The following quotations from the reports of Shamel and his associates will 
make clear the results of their investigation: "Thirteen important strains [of 
Washington Navel orange] have been found in the investigational performance 
record plots." 132 

"Twelve important strains of the Valencia variety have been found and 
described:" 133 "The lowest percentage of off type tree, i.e. marked variations 
from the best or Washington strain, found in commercial orchards have been 
about 10 per cent., and the highest about 75 per cent., of the total number of 



604 FUNDAMENTALS OF FRUIT PRODUCTION 

trees in the orchard." 132 "Tree-census observations in Navel orange orchards 
in California show a general average of about 25 per cent, of trees of diverse 
strains, most of which are inferior to the Washington as regards both the amount 
and the commercial quality of the fruit." 

"Occasional limbs have been found in such trees [Washington strain] pro- 
ducing typical Golden Nugget fruits consistently from year to year during the 
entire period of observation. . . . The variation in the amount of annual 
crops produced by a given series of individual Washington Navel orange trees 
is relatively uniform throughout the series each year. That is, the highest 
producing trees in any one year are in general the highest producing ones each 
year, and the lowest ones remain at the bottom of the list continually. Indi- 
vidual trees are relatively very stable over a series of years in the character and 
the amount of their production. . . . Suckers, or unusually vigorous non- 
bearing branches have been used almost universally for this purpose. This 
practice has led to the propagation of a continually increasing proportion of 
trees of those strains producing the largest amount of sucker growth. Inasmuch 
as such trees are usually light bearers and produce inferior fruits this practice 
has been unfortunate and is the direct cause of the presence of the large propor- 
tion of unproductive trees found in many orchards. Fruit bearing bud wood has 
been selected from limb variations occurring in trees of the Washington or other 
strains and in several hundred cases where the growth from these buds has 
fruited every selection has come true." 132 

With such fruits pedigreed is to be preferred to common stock for it 
represents definite types of strains that run true, when there is consider- 
able uncertainty as to what to expect from the general run of unselected 
stock. Perhaps "pedigreed" is an unfortunate term to apply to such 
selected stock; it is rather "improved" stock. 

Some Results with Apples. — Hedrick 74 represents fairly well one school 
of opinion when he says, concerning "pedigreed" apples: 

"At the very outset it must be pointed out that the seeming analogy between 
plants propagated from buds and cions and those grown from seeds has given a 
false simplicity to the fact and has led many astray. Analogy is the most 
treacherous kind of reasoning. We have here a case in which the similarity of 
properties is suggested but the two things are wholly different upon close analysis. 
In the case of seeds there is a combination of definite characters, in the offspring 
from two parents. Since the combinations of characters handed down from 
parents to children are never the same, individual seedlings from the same 
two plants may vary greatly. On the other hand, a graft is literally a ' chip of the 
old block' and while plants grown from buds may vary because of environment 
they do not often vary through heredity. . . The Geneva Station has an 
experiment which gives precise evidences upon this question of pedigreed stock. 
Sixteen years ago a fertilizer experiment was started with 60 Rome trees propa- 
gated from buds taken from one branch of a Rome tree. Quite as much varia- 
tion can be found in these trees from selected buds as could be found in an orchard 
of Romes propagated indiscriminately and growing under similar condition. 
Data showing the variations in diameter of tree and in productiveness . . . 



THE ROOT SYSTEMS OF FRUIT PLANTS 



605 



will go far to convince anyone that uniformity of behavior as regards vigor and 
productiveness of tree and size and color of fruit cannot be perpetuated." 

In 1895 the Missouri Station propagated from the highest and from the 
lowest yielding trees in an orchard of over 200 Ben Davis then in full 
bearing. The resulting trees were planted alternately in orchard rows 
and individual yield records were kept from 1912 to 1918 inclusive. These 
are summarized in Table 9, which shows no difference in favor of trees 
propagated from the best tree. Though there was a difference in size and 
finish of the fruit in the original trees there was none in the fruit borne by 
their offspring. Investigations in Vermont, reported by Cummings, 46 
show no consistent superiority in cions from superior trees of several 
varieties of apple. 

Table 9. — Average Yields of Apple Trees Propagated from High-yielding 

and from Low-yielding Parents 

(After Gardner™) 





From "good" parent 


From "poor" parent 




(bushels) 


(bushels) 


1912 


6.1 


5.4 


1913 


7.0 


11.3 


1914 


10.2 


6.3 


1915 


7.1 


10.3 


1916 


4.7 


8.1 


1917 


11.4 


6.6 


1918 


4.2 


11.8 


Average 


7.2 


8.5 



The statement has often been made that cion wood taken from 
certain parts of the tree gives rise to trees that are better than those pro- 
pagated from less carefully selected wood. Crandall 45 has given this 
matter thorough investigation in the apple and reports the following 
conclusions : 

"Summarized data giving comparisons between trees propagated from large 
buds and those propagated from small buds, together with the aggregate of 
impressions derived from careful inspections of trees of all groups, admit but one 
conclusion, namely, that there are no differences, for purposes of propagation, 
between buds of large size and those of small size. 

"Growth curves of trees propagated from buds of different situations on the 
trees so closely approximate as to leave no basis for assuming that it makes 
any difference from what situation on the tree the buds are taken. 

"All buds from healthy shoots are of equal value for purposes of propagation, 
at least so far as growth of tree is concerned. 



606 FUNDAMENTALS OF FRUIT PRODUCTION 

"Fluctuations in growth of individuals within particular groups are decided, 
often extreme. In general, differences become less with increase in age, provided 
the trees remain healthy. 

"There is no tangible basis upon which to establish the assumption that 
robust scions are superior to scions of small diameter for purposes of pro- 
pagation." 

These conclusions apparently differ from those of Shamel, Scott and 
Pomeroy working with citrus fruits. However, it should be noted that 
sucker growth was found in great abundance only in citrus trees that were 
"off type" individuals and it was to trees from such parentage that these 
workers particularly referred. In other words it was only because excess- 
ive sucker growth was correlated with a certain type of degeneration that 
propagation from wood of that kind yielded unsatisfactory results in 
practice. The evidence seems to warrant the conclusion that normal 
buds, whether borne on slow or rapid growing shoots or on suckers, are 
satisfactory for propagation, provided they are healthy and do not come 
from limbs that are bud mutations. Furthermore, it justifies the nursery- 
man in propagating from the nursery row, i.e., from young trees, provided 
there is no question of identity. 

In General. — At present comparatively little is known as to the extent 
of bud mutation within the various fruit groups. It is possible that 
opinions regarding pedigreed trees may need revision. Considering the 
present state of knowledge the prospective purchaser should ascertain 
accurately just what is meant by the term "pedigreed" stock in each 
case, the extent to which such nursery stock differs from the ordinary in its 
source and in its later performance record. Not until then can he tell how 
to reckon its comparative value. 

There is no doubt that occasional variations occur and can be per- 
petuated, but there is also no doubt that much of the variation between 
trees in the same orchard is due to soil variations or to differences in 
stocks and that these variations are not perpetuated. The fact that stock 
is propagated from a superior individual indicates a bare possibility that 
it is superior but it does not establish a probability that it is, much less 
a certainty. 

Suggested Collateral Reading 

Webber, H. J. Selection of Stocks in Citrus Propagation. Calif. Agr. Exp. Sta. 

Bui. 317. 1920. 
Burbidge, A. F. W. The Propagation and Improvement of Cultivated Plants. 

Pp. 57-86. London, 1877. 
Bonns, W. W., and Mertz, W. M. Experiments with Stocks for Citrus Calif. 

Agr. Exp. Sta. Bui. 267. 1916. 
Bioletti, F. T. Grape Culture in California. Calif. Agr. Exp. Sta. Bui. 197. 1908. 
Bioletti, F. T. Resistant Vineyards. Calif. Agr. Exp. Sta. Bui. 180. 1906. 



PROPAGATION 607 

Hedrick, U. P. Grape Stocks for American Grapes. N. Y. Agr. Exp. Sta. Bui. 355. 

1912. 

Hatton, R. G. Suggestions for the Right Selection of Apple Stocks. Jour. Roy. 

Hort. Soc. 45: 257-268. 1920. 

Literature Cited 

1. Allen, W. J. New South Wales Dept. Agr. Farmers' Bui. 86. 1914. 

2. Baco, F. Trav. sci. Univ. Rennes. 10 (2): 88-90. 1911. 

3. Ibid. 10 (2) : 97. 

4. Ibid. 10 (2) : 152. 

5. Ibid. 10 (2) : 158. 

6. Ibid. 10 (2) : 175. 

7. Bailey, L. H. Cornell Univ. Agr. Exp. Sta. Bui. 71. 1894. 

8. Bailey, L. H. Stand. Cycl. Hort. 3: 1363. New York, 1917. 

9. Bailey, L. H. Nursery Manual. P. 167. New York, 1920. 

10. Baltet, C. L'Art de Greffer. P. 7. Paris, 1902. 

11. Ibid. P. 119. 

12. Ibid. P. 211. 

13. Ibid. P. 369. 

14. Ibid. P. 415. 

15. Ibid. P. 453. 

16. Barry, P. Horticulturist. 3:136. 1848. 

17. Barry, P. The Fruit Garden. P. 303. Detroit, 1853 

18. Ibid. P. 310. 

19. Barss, H. P. Ore. Agr. Exp. Sta. Bienn. Crop Pest and Hort. Rept. 1:213. 

1913 

20. Berckmanns, P. J. Proc. Am. Pom. Soc. P. 70. 1881. 

21. Biff en, R. H. Ann. Bot. 16: 174. 1902. 

22. Bioletti, F. T. Cal. Agr. Exp. Sta. Bui. 197. 1908 

23. Bioletti, F. T. Cal. Agr. Exp. Sta. Bui. 180. 1906. 

24. Bioletti, F. T., and dal Piaz, A. M. Cal. Agr. Exp. Sta. Bui. 127. 1900. 

25. Blunno, M. New South Wales Dept. Agr. Farmers' Bui. 80. 1914. 

26. Bonns, W. W., and Mertz, W. M. Cal. Agr. Exp. Sta. Bui. 267. 1916. 

27. Bradford, F. C. Nat. Nurseryman. 29:152. 1921. 

28. Brown, B. S. Modern Propagation of Tree Fruits. P. 157. New York, 1916. 

29. Ibid. P. 160. 

30. Brown, W. R. Agr. Res. Inst. Pusa Bui. 93. 1920. 

31. Budd, J. L. la. Hort, Soc. Proc. 14: 464. 1879. 

32. Budd, J. L. la. Agr. Exp. Sta. Bui. 10. 1890. 

33. Burbidge, F. W. Propagation and Improvement of Cultivated Plants. P. 59. 

London, 1877. 

34. Ibid. P. 60. 

35. Ibid. P. 69. 

36. Ibid. P. 264. 

37. Ibid. P. 267. 

38. Cock, S. A. Jour. Dept. Agr. Victoria. 11:372. 1913. 

39. Ibid. 11:714. 

40. Cole, C. F. Jour. Dept. Agr. Victoria. 9. 1911. 

41. Condit, I. J. Cal. Agr. Exp. Sta. Bui. 250. 1915. 

42. Corsa, W. P. Nut Culture in the United States. P. 80. Washington, 1896. 

43. Coulter, J. L, Barnes, C. R., and Cowles, H. C. Text Book of Botany. 2:777. 

New York, 1911. 



608 FUNDAMENTALS OF FRUIT PRODUCTION 

44. Ibid. 2: 779. 

45. Crandall, C. S. 111. Agr. Exp. Sta. Bui. 211. 1918. 

46. Cummings, M. B. Vt. Agr. Exp. Sta. Bui. 221. 1921. 

47. Curtel, G. Compt. rend. 139: 491. 1904. 

48. Daniel, L. Compt. rend. 114: 1294. 1892. 

49. Ibid. 136: 1157. 1903. 

50. Daniel, L. Trav. sci. Univ. Rennes. 2: 73. 1903. 

51. Ibid. 2: 173. 

52. Ibid. 2: 210. 

53. Daniel, L. Rev. hort. 10 (N.S.): 469. 1910. 

54. Ibid. 13 (N.S.): 348. 1913. 

55. Ibid. 14 (N.S.): 135. 1914. 

56. Darwin, C. Animals and Plants under Domestication. 2: 266. New York. 

1894. 

57. Dawson, J. Mass. Hort. Soc. Trans. P. 123. 1895. 

58. Ibid. P. 134. 

59. Dental, J. B. Rev. hort. 16 (N.S.): 47. 1916. 

60. Downing, A. J. Fruits and Fruit Trees of America. P. 25. New York, 1856. 

61. Duplessix. Trav. sci. Univ. Rennes. 10 (2): 5. 1911. 

62. Ibid. 10 (2) : 18. 

63. Ibid. 10 (2) : 38. 

64. Ibid. 10 (2) : 192. 

65. Gardner, V. R. Mo. Agr. Exp. Sta. Res. Bui. 39. 1920. 

66. Gould, H. P. U. S. D. A. Farmers' Bui. 776. 1916. 

67. Hansen, N. E. S. D. Agr. Exp. Sta. Bui. 87. 1904. 

68. Hansen, N. E. S. D. Agr. Exp. Sta. Bui. 93. 1905. 

69. Harwell, R. Horticulturist. 5: 257. 1850. 

70. Hatton, R. G. Jour. Roy. Hort. Soc. 45 (2): 257. 1919-1920. 

71. Ibid. 45 (2). 269. 

72. Hedrick, U. P. Plums of New York. P. 115. Albany, 1911. 

73. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 355. 1912. 

74. Hedrick, U. P. N. Y. Agr. Exp. Sta. Cir. 18. 1912. 

75. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 406. 1915. 

76. Hedrick, U. P. Cherries of New York. P. 72. Albany, 1919. 

77. Hendrickson, A. H. Cal. Sta. Dept. Agr. Mo. Bui. 4: 171-174. 1918. 

78. Horticulturist. 6:337. 1851. 

79. Ibid. 6:374. 

80. Howard, A., and Howard, G. L. C. Sci. Rept. Agr. Inst. Pusa. P. 48. 1916- 

1917. 

81. Howard, W. L. Cal. Board Hort. Mo. Bui. 9: 3. 1920. 

82. Hume, H. H. Fla. Agr. Exp. Sta. Bui. 71. 1904. 

83. Husmann, G. C. U .S. D. A., Bur. PL Ind. Bui. 172. 1910. 

84. Husmann, G C. U. S. D. A., Bui. 856. 1920. 

85. la. Agr. Exp. Sta. Ann. Rept, P. 33. 1919. 

86. Jost, L. Pflanzenphysiologie. 3te. Auflage. P. 448. Jena, 1913. 

87. Kelly, W. P., and Thomas, E. E. Cal. Agr. Exp. Sta. Bui. 318. 1920. 

88. Knight, T. A. Phys. and Hort. Papers. P. 155. London, 1841. 

89. Ibid. P. 223. 

90. Ibid. P. 273. 

91. Ibid. P. 274. 

92. Laurent, C. Trav. sci. Univ. Rennes. 8: 37. 1909. 

93. Lawrence, J. Clergyman's Recreation. P. 64. London, 1717. 

94. Leclerc du Sablon. Compt. rend. 136: 623. 1903. 



PROPAGATION 609 

95. Lindemuth, H. Landw. Jahrb. 7: 909. 1878. 

96. Ibid. 7: 912. 

97. Lindemuth, H. Ber. Bot. Gesel. 19: 515. 1901. 

98. Ibid. 19: 527. 

99. Lindley, J. Theory and Practice of Horticulture. P. 355. London, 1855. 

100. Livingstone, J. Trans. Hort. Soc. London. 4: 231. 1822. 

101. Loudon, J. C. The Horticulturist. P. 283. London, 1860. 

102. Lucas, E. Die Lehre vom Baumschnitt. P. 37. Ravensburg, 1874. Cited in 

Lindemuth, H., Landw. Jahrb. 7: 911. 1878. 

103. Macdonald, L. Jour. Dept. Agr. Victoria. 10: 69. 1912. 

104. Macoun, W. T. Cent. (Can.) Exp. Farms. Bui. 38. 1907. 

105. Manning, R. Mass. Hort. Soc. Trans. P. 37. 1879. 

106. Mass. Hort. Soc. Trans. Pp. 6-43. 1879. 

107. Maynard, S. T. Hatch (Mass.) Agr. Exp. Sta. Bui. 17. 1892. 

108. Maynard, S. T. Successful Fruit Culture. P. 74. New York, 1909. 

109. Ibid. P. 197. 

110. Mills, J. W. Cal. Agr. Exp. Sta. Bui. 138. 1902. 

111. Moore, J. G. Proc. Am. Soc. Hort. Sci. 16: 84. 1919. 

112. Murneek, A. L. Better Fruit. 15: No. 7. 1921. 

113. Neer, F. E. Correspondence. 1921. 

114. Noisette, L. Vollstand. Handb. der Gartenkunst. Uebersetzt von Sigwart. 

Stuttgart. 1826. 

115. Oberdieck. Illus. Monatshefte fur Obst- und Weinbau. P. 44. 1873. 

Cited by Lindemuth, H., Landw. Jahrb. 7: 909. 1878. 

116. Onderdonk, G. Proc. Am. Pom. Soc. P. 92. 1901. 

117. Pepin. Rev. hort. Ser. 3. 2: 183. 1848. 

118. Proc. Am. Pom. Soc. 1881. 

119. Proc. Am. Pom. Soc. P. 128. 1889. 

120. Reimer, F. C. Ann. Rept. Pac. Coast Assoc. Nurserymen. 1916. 

121. Rivers, T. The Miniature Fruit Garden. P. 103. New York, 1866. 

122. Riviere, G. et Bailhache, G. Compt. rend. 124: 477. 1897. 

123. Roeding, G. C. Fruit Growers' Guide. P. 18. Fresno, 1919. 

124. Ibid. P. 20. 

125. Ibid. P. 26. 

126. Rolfs, P. H. Fla. Agr. Exp. Sta. Bui. 127. 1915. 

127. Sahut, F. Rev. hort. 57: 149. 1885. 

128. Ibid. 57: 201. 

129. Ibid. 57: 258. 
1*30. Ibid. 57: 305. 

131. Ibid. 57: 398. 

132. Shamel, A. D. et at U. S. D. A., Bui. 623. 1918. 

133. Shamel, A. D. et al. U. S. D. A., Bui. 624. 1918. 

134. Shaw, J. K. Proc. Am. Soc. Hort. Sci. 14: 64. 1917. 

135. Shaw, J. K. Science. 45 (N.S.); 461. 1917. 

136. Shaw, J. K. Mass. Agr. Exp. Sta. Bui. 190. 1919. 

137. Shaw, J. K. Correspondence. 1921. 

138. Sorauer, P. Manual of Plant Diseases. 3d ed. (transl.) 1: 841. Wilkes- 

barre, 1920. 

139. Stuart, W. Vt. Agr. Exp. Sta. Ann. Rept. 18: 300. 1905. 

140. Swingle, W. T. U. S. D. A., Bur. PL Ind. Cir. 46. 1909. 

141. Talbot, J. Mass. Hort. Soc. Trans. P. 6. 1879. 

142. Taylor, R. H. Cal. Agr. Exp. Sta. Bui. 297. 1918. 

143. Tufts, W. P. Correspondence. 1921. 

39 



610 FUNDAMENTALS OF FRUIT PRODUCTION 

144. Vard, E. Rev. hort. 63: 514. 1891. 

145. Victoria Jour. Dept. Agr. 14: 6. 1916. 

146. Voechting, H. Cited by Lindemuth, H. Ber. Bot, Gesel. 19: 515. 1901. 

147. Vosbury, E. D. U. S. D. A. Farmers' Bui. 1122. 1920. 

148. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 13: 333. 1900. 

149. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 14: 259. 1901. 

150. Waugh, F. A. Plums and Plum Culture. P. 238. New York. 1910. 

151. Webber, H. J. Cal. Agr. Exp. Sta. Bui. 317. 1920. 

152. Webber, H. J. el al. Cal. Agr. Exp. Sta. Bui. 304. 1919. 

153. Wickson, E. J. California Fruits. P. 246. San Francisco. 1910. 

154. Ibid. P. 345. 

155. Ibid. P. 439. 

156. Wisker, A. L. Cal. Board Hort, Mo. Bui. 5: 112. 1916. 



SECTION VII 
GEOGRAPHIC INFLUENCES IN FRUIT PRODUCTION 

Perseverance has not only developed fruits with qualities superior 
to those of the wild; it has extended their growth into regions to which 
they are not native. The two most important orchard fruits of the 
United States are not indigenous. Social and economic conditions have 
played no unimportant parts in developing fruit growing or in preventing 
its development. Transportation facilities or neighboring markets are 
of utmost importance. Necessary as these all are, however, they can 
not establish a fruit growing industry unless its development is possible 
under the complex of natural influences which are grouped conveniently 
under the term geographic. Though complete analysis of this complex 
is impossible, since one factor's influence may be modified by that of 
another factor, some general statements can be made with safety. 

A knowledge of the conditions which favor, interfere with or prevent 
fruit growing at various points may be of considerable value for local 
application, since it may suggest the capitalization of certain features of 
the local climate through the growing of fruits best suited to those condi- 
tions or it may indicate certain departures of the local climate from the 
best conditions for a given fruit, necessitating particular care in some 
phase of management. Furthermore, it may suggest to the plant breeder 
definite aims in improvement to secure adaptation or possibly it may 
indicate sources of material with which he can work most profitably. 
Plant improvement for one section may be quite different from the 
amelioration necessary in the same fruit for another. 



611 



CHAPTER XXXIII 
THE GEOGRAPHY OF FRUIT GROWING 

Certain fruits like the apple are grown throughout most of the tem- 
perate regions of both hemispheres, the industry in the case of the apple 
reaching its height in the northern half of the United States and Europe 
and in the southern part of Australia, Tasmania and New Zealand. The 
pear is cultivated throughout practically the same range; its quantity 
production is much more localized. Sweet cherry production is developed 
mainly in the western nations of Europe and the western states of North 
America. None of these fruits is of great importance in South America, 
though the grape, which is grown along with the apple and pear in North 
America, Europe, Asia and Australia is an extremely important fruit 
on that continent. On the other hand, certain fruits have very restricted 
geographic ranges. The date is grown mainly in countries bordering the 
Mediterranean, the jaboticaba in parts of Brazil, the jujube in central 
China, the pecan in the southeastern United States, the loganberry in 
Washington, Oregon and California. The accompanying maps (Figs. 
59 to 64) present graphically a few interesting facts regarding the geo- 
graphic distribution of certain of the more common fruits. Incidentally 
Figs. 59 and 60, representing total apple production and total number of 
apple trees of bearing age in the United States in 1909, show that actual 
production is often not proportional to tree number. 

The distribution of individual varieties is equally interesting. For 
instance the Fameuse apple is of great importance in the St. Lawrence 
river region, the Yellow Bellflower in parts of California, the Huntsman 
in Missouri; Yellow Newtown is important in New York, Virginia, 
Washington, Oregon, California, Tasmania and New South Wales. 

It is one thing to construct a map which shows the geographic dis- 
tribution of various fruits; it is quite another to find the exact reasons for 
this distribution. Without doubt many factors are operative. Some 
are of relatively great, others of much less, importance. A single factor 
may be decisive with one fruit, an entirely different factor with another 
and a group of several factors may be of almost equal importance in a 
third case. 

LIFE ZONES, CROP ZONES AND FRUIT ZONES 

In a broad way the fruit zones of the world coincide more or less closely 
with the general life zones and crop zones, though the pomologist may use 

612 



THE GEOGRAPHY OF FRUIT GROWING 



613 




614 



FUNDAMENTALS OF FRUIT PRODUCTION 



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THE GEOGRAPHY OF FRUIT GROWING 



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616 



FUNDAMENTALS OF FRUIT PRODUCTION 




THE GEOGRAPHY OF FRUIT GROWING 



617 



other names to designate them than the biological cartographer does. 

These general life zones as determined for the United States, southern 

Canada and northern Mexico 

by the Bureau of Biological 

Survey of the United States 

Department of Agriculture, are 

shown in Fig. 65. 

The Boreal Zone. — As here 
outlined, the Boreal zone or 
region includes all of Canada 
except a portion of Nova 
Scotia, a strip along the St. 
Lawrence River and running 
west through Ontario to Lake 
Huron and Georgian Bay, 
southern Saskatchewan and 
limited areas in southern 
Manitoba, Alberta and British 
Columbia. Its southern boun- 
dary dips down into the United 
States so as to include parts of 
northern New England, north- 
ern Michigan, a small strip of 
northeastern Wisconsin and a 
considerable part of Minnesota 
and North Dakota. Irregular- 
ly shaped areas characterized 
by the life of the Boreal region 
are found here and there in 
New York and Pennsylvania 
and at some of the higher eleva- 
tions of the Allegheny Moun- 
tains as far south as southern 
Tennessee. In the western 
parts of the United States 
there are finger-like projections 
of this region and isolated areas 
with its characteristic fauna 
and flora extending as far south 
as the state of Zacatecas in 
Mexico. For the most part these extreme southern extensions are limited 
to the higher elevations of the Rocky, Sierra Nevada, Cascade and Coast 
mountain ranges. Its southern limit is marked by the isotherm of 18°C. 
(64.4°F.) for the six hottest consecutive weeks of midsummer. 45 On the 




618 



FUNDAMENTALS OF FRUIT PRODUCTION 



whole this region is not suited to fruit growing; nevertheless a number of 
fruits are thoroughly at home and indeed reach their best development 




along its southern borders, 
currant and gooseberry. 



Among these are the cranberry, blueberry, 



THE GEOGRAPHY OF FRUIT GROWING 619 

The Tropical Zone. — Only a very small part of the continental United 
States is included within the Tropical region or zone. To be exact, there 
are three widely separated areas where tropical conditions prevail and 
tropical vegetation abounds — one in southern Florida, one in extreme 
southeastern Texas, and one along the California-Arizona line, extending 
as far north as southern Nevada. Within these areas are such fruits as 
the banana, pineapple, mango, date palm, cocoanut, papaya and cheri- 
moya. This region is never visited by frosts or freezing temperatures and 
many of the fruits grown in it are said to be seriously injured by tempera- 
tures even closely approaching the freezing point. To the pomologist, 
as to the biologist, this region is known as the Tropical zone. It is char- 
acterized by having more than 14,400°C. (26,000°F.) of heat during the 
year — degrees of normal mean daily heat in excess of a minimum of 6°C. 
(43°F.), 45 which is rather arbitrarily assumed as marking the inception 
of physiological activity in plants. 

Austral or Temperate Zone. — Between the Boreal region on the north 
and the Tropical region on the south and embracing most of the area of the 
United States, is a region designated as Austral on the maps of biological 
surveys and designated as the Temperate zone by the pomologist. Frosts 
and freezes are likely to occur throughout most of this region, but mini- 
mum winter temperatures seldom go below — 30°F. at the north and the 
mean temperature of midwinter months even of the more northern 
sections is well above zero. 

Transition Zone. — Biologists recognize three transcontinental life 
zones within this region, a so-called Transition zone to the north and an 
Upper Austral and Lower Austral zone to the south. Some of the more 
hardy fruits, as the apple, pear, red raspberry and the Nigra and European 
groups of plums find their most congenial home in the Transition zone. 
In the east this zone includes most of those portions of New England, 
New York, Pennsylvania and Michigan and in the middle west most of 
those portions of Wisconsin, Minnesota and the Dakotas not included 
in the Boreal region; in the west it includes many irregularly shaped 
areas from the Canadian border to Mexico, and even in Mexico, where 
elevation causes comparatively low temperatures. "Transition zone 
species", Merriam states, "require a total quantity of heat of at least 
5500°C. (10,000°F.) but can not endure a summer temperature the mean 
of which for the six hottest weeks exceeds 22°C. (71.6°F.) The northern 
boundary of the Transition zone, therefore, is marked by the isotherm 
showing a sum of normal positive temperatures of 5,500°C. (10,000°F.), 
while its southern boundary is coincident with the isotherm of 22°C. 
(71.6°F.) for the six hottest consecutive weeks." 45 

This Transition zone is in turn divided into three areas by lines having 
a general north and south direction, areas that differ from one another 
primarily ,in rainfall and atmospheric humidity. The eastern area, 



620 FUNDAMENTALS OF FRUIT PRODUCTION 

known as the Alleghanian, extends from the Atlantic seaboard approxi- 
mately to the 100° meridian, which runs through central North and South 
Dakota, Nebraska and Texas. To the west of this is a central arid area 
extending to the Sierra Nevada-Cascade mountain range. West of this 
is the Pacific coast humid area, very humid at the north but toward the 
south gradually merging into the conditions presented by the central 
arid area. Generally speaking, the same fruit species thrive in all of these 
areas, though they cannot be grown without irrigation in the central 
arid section. However, though the same fruit species are grown in all 
three areas the same varieties are not equally successful; consequently 
each area has a more or less distinctive variety flora. 

Upper Austral Zone. — The Upper Austral region includes a compara- 
tively narrow belt of territory in the central Atlantic States but widens 
out to include a comparatively large part of the corn belt area in the 
middle west and like the Boreal and Transition regions it includes many 
irregularly shaped areas from the Canadian line to far below the Mexican 
border. According to Merriam: " Upper Austral species require a total 
quantity of heat of at least 6,400°C. (11,500°F.), but apparently cannot 
endure a summer temperature the mean of which for the six hottest 
consecutive weeks exceeds 26°C. (78.8°F.). The northern boundary of 
the Upper Austral zone, therefore, is marked by the isotherm showing a 
sum of normal positive temperatures of 6400°C. (11,51 1°F.) while its 
southern boundary agrees very closely with the isotherm of 26°C. 
(78.8°F.) for the six hottest weeks." 45 The eastern half of this zone, 
known as the Carolinian area, has a humid climate; the western half, 
known as the Upper Sonoran area, is comparatively arid. The walnut, 
hickory, sassafras, sycamore, red bud and papaw are typical native 
trees of the Carolinian area; the sage brush, greasewood and juniper 
characterize the Upper Sonoran. Within this zone the peach, the 
Japanese plum, the persimmon and many varieties of the apple, pear, 
cherry and grape attain their highest development. 

Lower Austral or Subtropic Zone. — The Lower Austral zone lies 
between the Upper Austral and Tropical regions. On the east it includes 
most of the south Atlantic seaboard and in the Mississippi valley it 
extends north into southern Missouri, Illinois and Indiana; in the west 
it includes most of southern California and much of the Sacramento and 
San Joaquin valleys. Merriam states: "Lower Austral species require a 
total quantity of heat of at least 10,000°C. (18,000°F.)." 45 Like the 
Upper Austral zone, its eastern half has a humid and its western half an 
arid climate. The eastern half is known as the Austroriparian area, the 
western half as the Lower Sonoran. The former is characterized by such 
native vegetation as the long-leaf and loblolly pines, the magnolia, the 
live oak and the pecan. It is a rich agricultural area producing cotton, 
rice, sugar cane and many other warm season crops. The distinctive 



THE GEOGRAPHY OF FRUIT GROWING 621 

fruits of its more northern reaches are the pecan, the muscadine grapes 
and pears of the oriental hybrid class. The Lower Sonoran area is 
characterized by many cacti, yuccas, agaves, mesquites and other desert 
plants. It produces plums, prunes, peaches, cherries, apricots, almonds, 
grapes and many other fruits in great quantities where irrigation water is 
available. The southern part of the Lower Austral zone is known to the 
pomologist as the Subtropic zone. Horticulturally it is one of the most 
important in the United States. Within it are produced citrus fruits, 
figs, avocados, loquats, Japanese persimmons and many other less 
known fruits. 

Attention may be directed to the fact that the boundaries of the 
pomological districts of the United States, as they have been mapped by 
the American Pomological Society do not coincide exactly with those of 
the life zones that have been discussed, though the two maps have many 
features in common. 



GEOGRAPHY OF FRUIT PRODUCTION AS INFLUENCED BY TEMPERATURE 

It will be noted that these life zones or crop zones include areas charac- 
terized by a certain uniformity of climate and that, of all the features 
that constitute climate, temperature is given first consideration. Indeed 
the boundaries of the different regions and zones are for the most part 
isothermals, and the main reason for such irregular outlines, especially 
in the mountainous districts, is the influence of altitude upon temperature. 
High altitude through its accompaniment low-temperatur, accounts for 
the island-like areas of the Boreal or Transition zones in latitudes gen- 
erally dominated by the life of the Austral. Generally there is a lower- 
ing of about 4°F. in mean temperature for each increase in elevation 
of 1,000 feet. Even at the equator frost will occur at an elevation of 
about 18,000 feet; on the island of Hawaii, at a latitude of 20° North, 
frost occurs at an altitude of 4,500 feet or above. 64 

Temperature here is meant to include not only the mean annual 
temperature but also the minimum and maximum temperatures of 
winter, spring, summer and autumn, respectively, the mean temperature 
month by month, particularly through the growing season, the occurrence 
of frost during the critical period just before, during and just after, 
blossoming, the length of the growing season (see Fig. 66), the evenness 
of temperature from day to day, and many other characteristics of the 
weather that are more or less directly attributable to temperature 
changes. Sometimes it is one of these features of temperature, e.g., 
minimum winter temperature, or mean temperature during the growing 
season, that sets the limits for a certain fruit; sometimes it is another. 
Broadly speaking it is the minimum winter temperatures that set northern 



622 



FUNDAMENTALS OF FRUIT PRODUCTION 



limits to the production of fruits of particular kinds and mean rather than 
maximum temperatures during four to six weeks of the warmest weather, 
that set their southern limits. 45 There are, however, numerous 
exceptions. 




Fig. 66. — Computed length of available growing season 4 years in 5. (After Reed) 



Peach Growing as Influenced by Temperature. — The varying in- 
fluences of temperature on the geographic range of fruits are shown 
clearly by the peach, if comparison be made between Europe and the 
United States. Table 1 shows mean monthly temperatures at selected 
points. Bordeaux, Perpignan, Montpellier and Lyons in France may be 
considered to have temperatures favorable to peach growing. Roscoff, 
in Brittany, Plymouth, England, and Bergen, Norway, are in regions 
where few or no peaches are grown, though they are warmer in winter than 
Rochester, New York, which is typical of much of the peach-growing area 
in the northeastern states. The difference between the points named 
where peach growing is successful and those where it is not lies in the sum- 
mer temperatures. So far as winter temperature is concerned peaches 
apparently could be grown in Berufjord, Iceland; deficiency in summer 
temperatures seems the limiting factor in a considerable part of 
Europe. 

Between Nashua and Concord, in New Hampshire, about 35 miles 
apart, runs the northern limit of commercial peach growing in that section. 
Examination of the table shows only small differences in mean monthly 



THE GEOGRAPHY OF FRUIT GROWING 623 

temperatures; the absolute minima for the two stations are, respectively, 
— 25°F. and — 35°F. Near the one point commercial peach growing is 
profitable; a few miles away it becomes unprofitable. The July tempera- 
ture for Concord is identical with that for Fitchburg, Mass. (cf. Table 
3), well within the zone of peach growing, and greater than that of 
Roseburg, Ore. Apparently, then, for conditions obtaining in southern 
New Hampshire, the northern limit of commercial peach production is 
set by winter temperatures averaging between those for the two stations 
given. 

Pierre, S. D., has as high or higher summer temperatures than many 
sections where the peach grows readily, but its winter temperatures are 
too low. Near Portland, Maine, the peach reaches its limit in ordinary 
cultivation and is subject to winter injury. Portland, Ore., with a summer 
temperature slightly lower, provides, through milder winters, conditions 
such that the peach grows fairly well. Near Lincoln, Neb., the peach 
grows about as at Portland, Maine; though the winter temperature 
averages a shade lower, the summer is warmer, suggesting a greater 
maturity in the fall with consequent ability better to withstand the winter. 
This, however, is the only way in which summer temperature may be 
considered to influence peach growing in any large area of the United 
States. The chief limiting temperature factor here comes in the winter. 
Nevertheless the factor of summer temperature or the length of the grow- 
ing season may become important in isolated areas along the northern 
border of peach growing. 

Grape Growing as Influenced by Temperature. — The northern limit 
of grape culture, as with the peach, is set by summer temperatures at 
some points and by winter temperatures at others. Its course in Europe 
has been defined as extending "from somewhat north of the mouth of the 
Loire, where the Marne empties into the Seine, to the junction of the Aar 
and the Rhine, north of the Erzgebirge, to about the 52° of latitude, 
descends along the Carpathians to the 49°, extends on this parallel east- 
ward, and near the Volga turns southward to its mouth, in the Caspian 
Sea." 11 

Wine in considerable quantities was made north of this line, in Eng- 
land, and even in Zeeland, in former times. This fact, sometimes cited 
as proving a change in climate probably proves no more than a change in 
taste. " It must be taken for granted that in those times when there was 
no communication over long distances they were not very exacting in 
regard to wine, particularly as the best wines were unknown, as must 
have been the case in northern Germany, the Netherlands and England. 
If the wine was harsh and sour, it was still wine. . . . With the 
present facilities for communication and the competition in the wine 
business resulting therefrom; vine culture is no longer profitable in many 
places where 30 years ago it was so; . . ." 



624 



FUNDAMENTALS OF FRUIT PRODUCTION 



The boundary thus set, therefore, is not necessarily the limit of the 
ability of the grape to grow; it does, however, mark the limit of its ability 
to ripen sufficiently for wine making. This line in western Europe is set 
by summer temperatures. In eastern Europe it is set by winter tem- 
peratures and does represent approximately the real limit of culture of 
the vine. 

Table 2 shows the mean monthly temperatures for a number of selected 
European stations. Some of these, for example, Bordeaux in France, 
Florence in Italy, Patras in Greece and Odessa in Russia, are either centers 
of important viticultural industries or they fairly represent such districts. 
Others, like Bergen in Norway, Plymouth in England and Roscoff in Brit- 
tany are places where outdoor grape culture for wine is impracticable. 

Table 1. — Mean Monthly Temperatures in Relation to Peach Growing 

(Degrees Fahrenheit) 

































a 


















Si 




J2 












-^ 


S 


o 


S 




ft 
< 


>> 

03 


a 

1-5 


>-3 


M 

< 


0) 
ft 
50 


o 
o 
O 


4) 
> 


'A 


47 


53 


58 


64 


68 


68 


64 


55 


47 


50 


56 


61 


68 


73 


72 


67 


58 


51 


48 


55 


61 


68 


73 


72 


65 


57 


48 


46 


50 


53 


58 


61 


62 


59 


55 


49 


44 


48 


53 


58 


61 


61 


58 


51 


47 


35 


42 


45 


55 


58 


58 


53 


45 


38 


46 


54 


60 


66 


70 


69 


63 


53 


44 


29 


34 


39 


44 


47 


47 


44 


38 


34 


32 


44 


57 


65 


70 


67 


60 


49 


37 


34 


46 


58 


67 


71 


68 


61 


49 


38 


31 


44 


57 


66 


70 


68 


62 


51 


38 


32 


43 


54 


63 


68 


66 


60 


49 


38 


46 


51 


57 


61 


66 


66 


61 


53 


46 


30 


46 


59 


69 


75 


73 


63 


49 


32 


36 


51 


63 


72 


76 


74 


65 


53 


38 



Bordeaux, France (1) . 
Perpignan, France (1) . 
Montpellier, France (1) 
Roscoff, France (1). . . . 
Plymouth, England (1) 
Bergen, Norway (1) 
Lyons, France (1) . . . . 
Berufjord, Iceland (1) . 

Concord, N. H. (2) 

Nashua, N. H. (2) . . . . 
Rochester, N. Y. (3). .. 
Portland, Maine (3) . . 
Portland, Ore. (3) 

Pierre, S. D. (3) 

Lincoln, Neb. (3) 



41 
45 
42 
46 
43 
35 
37 
30 
26 
28 
29 
27 
41 
20 
27 



1. Hann. J., Handb. der Klimatologie, Stuttgart (1911). 

2. United States Department Agriculture, Weather Bureau, Bui. Q. (1906). 

3. United States Department Agriculture, Weather Bureau, Bui. R. (1908). 

Yet these latter points have mean winter temperatures above those of 
some of the grape growing districts and their absolute minimum tempera- 
tures are likewise higher. However, their mean summer temperatures are 
comparatively low — too low for the grape to mature its fruit and wood 
properly; consequently the industry does not flourish there. 

Temperature and the Geographic Range of Apple Varieties. — The 
same general principles operate to establish limits for the profitable 
culture of different varieties of the same fruit. Thus, winter tempera- 
tures at Eastport, Maine, are higher than those at Lewiston, in the same 
state. The Baldwin apple grows very well around Lewiston but not at 
Eastport. The difference in suitability of the two places lies evidently 



THE GEOGRAPHY OF FRUIT GROWING 625 

in the summer temperatures. Madison, Wis., has evidently sufficient 
summer heat to satisfy the Baldwin's requirements; the difficulty in 
growing Baldwin at this last point is known to be winter temperature. 
So far as apple growing in the United States is concerned, then, there 
are along the northern limit, two different factors operating, summer 
temperature and winter temperature; the effects of the one sometimes 
mask those of the other. However, there appear to be very few places 
listed in the table where the Baldwin apple would suffer from lack of 
summer heat. Data are presented in Tables 3 and 4 showing the mean 
monthly temperatures throughout the year and the minimum tempera- 
tures for the six winter months at a number of stations in the United 
States. Except for the California and Alaska points, each station 
included in the tables may be taken as representing fairly well a commer- 
cial apple producing section. The figures afford an idea of the range in 
mean and minimum temperatures within which apple growing is profi- 
table and by inference, an idea of the temperature limits for the commer- 
cial varieties. A comparison of these data with the records of the 
leading varieties in the several districts represented, likewise affords a 
fairly accurate measure of their particular temperature requirements 
and this, in turn, may be used as a basis for judging their probable 
suitability for sections where they have not been tried but where tem- 
perature records are available. 

Averages are treacherous at times and caution should be observed 
in their interpretation. Lewiston, Maine, shows the lowest mean winter 
temperatures of any of the apple sections represented in Table 3. Never- 
theless this region grows successfully several apple varieties which cannot 
be grown in the Bitter Root valley, as represented by Missoula. Refer- 
ence to Table 4 shows that the mean temperatures for Missoula conceal 
a November minimum of — 20°F. as compared with plus 2°F. for Lewiston 
and a January minimum of — 42°F. for Missoula as compared with 
— 24°F. for Lewiston. Over a long period the amount of winter killing 
around Lewiston is probably no greater than that around Spokane, Wash., 
though Lewiston averages 8° colder in January and 10° colder in February. 
The October and November means, however, are only 1° apart. Abso- 
lute minima for Lewiston in October, November and January are actually 
higher than those for Spokane (6°, 15° and 6°F. respectively). The 
November temperatures, mean and minimum, seem particularly impor- 
tant in relation to winter injury along the northern border of apple 
growing. 

The total effective growing temperatures at Portland, Oregon, and 
Portland, Maine, are practically the same and the same varieties of 
apples attain an almost equal development in the two places. Appar- 
ently in this case neither maximum nor mean summer temperatures in 
Oregon nor minimum winter temperatures in Maine are limiting factors 

40 



626 FUNDAMENTALS OF FRUIT PRODUCTION 

in the growth of the varieties in question. Mean temperature during 
the growing season, therefore, in this case becomes an accurate index of 
adaptation to climate. 

On the other hand the loganberry and sweet cherry which thrive so 
well in the vicinity of Portland, Ore., cannot be grown profitably near 
Portland, Maine, because minimum winter temperature is a limiting 
factor. The blueberry, which grows so luxuriantly near Portland, Maine, 
fails to grow near Portland, Ore., not because temperature is a limiting 
factor but presumably because it does not find a congenial soil. 

Investigations in fruit growing at Sitka, Alaska, show interesting effects of 
a rather unusual climate. From November to March inclusive the mean tem- 
peratures are higher than those of Lewiston, Maine; they exceed those of Roches- 
ter, N. Y., for nearly the same period and for December to February they are 
somewhat higher than those of Martinsburg, W. Va. Zero temperatures are 
very rare; nevertheless winter killing is common. Records of the Alaska Agri- 
cultural Experiment Stations show that such hardy plums as De Soto and Roll- 
ingstone, numerous apple varieties selected for hardiness, the sand cherry and 
blackberries have suffered considerable injury. 

The causes of this condition are indicated in the following quotations from 
reports of the station: 

"Only early maturing sorts will succeed. Varieties which are summer 
apples in the States will be fall apples in Alaska, and those which are fall apples 
in the States will not mature at all in Alaska. The summer heat is not great 
enough. In the coast region the season between frosts is long — longer, indeed, 
by at least two months than in the northern tier of states. 

"In the larger portion of the coast region there is little, if any, damaging frost 
between May 1 and October 1, and some seasons damaging frosts do not occur 
until the end of October. The drawback to the climate in this region lies not 
in too great cold, but, anomalous as the statement seems, in the lack of summer 
heat. . . . The maximum temperature is more generally between 60° and 70°, 
and some summers it will not go much above 60°. In the interior, on the other 
hand, the summers are warm enough, at least in places but the season is too 
short to hope to mature any but the earliest sorts and there is considerable doubt 
if they will succeed." 13 

"The excessive rainfall and continuous mild weather prolongs the growing 
season until long into October. The young wood is soft and succulent, and 
moderately cold weather the following winter kills it." 14 

"The winter of 1908-1909 was quite severe for this part of the coast region. 
The temperature fell to 2° above zero and 3° above zero in January and Febru- 
ary, respectively, and the cold period was protracted over many weeks. As a 
consequence, the young growth produced in the season of 1908 was partly killed 
in most cases, and in some cases entirely." 16 

"Blackberries and dewberries cannot be grown successfully in any part of 
Alaska. They have been tried repeatedly at the Sitka Experiment Station and 
the attempt has always resulted in failure. The summer is not warm enough to 
develop the fruit and the plants usually winterkill even in mild winters, probably 
due to the late succulent growth resulting from the abundance of moisture." 16 



THE GEOGRAPHY OF FRUIT GROWING 



627 



Phenological data taken at Sitka are interesting. Apples are recorded as 
leafing out June 1; Early Richmond cherry in blossom June 15, the Whitney 

Table 2. — Mean Monthly Temperature at Selected European Stations 

{Compiled from Hann 18 ) 
(In degrees Fahrenheit) 





>> 




>1 






3 


3 




3 









o3 


03 

1-5 


Ph 


3 









9 






J2 




.a 


2 


3 

J3 


s 






> 
o 


0, 

go 


o 



Bordeaux, France . . 
Budapest, Hungary 
Patras, Greece . . . . 
Bremen, Germany. 
Plymouth, England 
Lemburg, Austria . . 
Roscoff, France .... 
Bergen, Norway . . . 

Florence, Italy 

Nantes, France 

Odessa, Russia 



40.6 
28.2 
51. 1 
33.6 
42.1 
24.3 
45.0 
34.2 
40.7 
40.1 
25.3 



42.9 
31.4 
53.0 
34.7 
42.8 
25.7 
44.8 
33.6 
42.1 
41.9 
27.7 



46.9 
39.9 
56.1 
38.1 
43.8 
31.1 
46.2 50. 
42. 1 48. 
48.9 56. 
45.2 51. 
34.9 47. 



64.2 
66.7 
74.5 
60.3 
58.4 
64.3 
57.7 
55.2 
70.7 
62.2 
68.0 



63.7 


55.4 


46.9 


61.1 


51.1 


40.2 


76.6 


69.8 


61.1 


56.5 


48.4 


39.4 


57.6 


51.1 


46.8 


57.0 


47.3 


34.7 


59.4 


55.2 


49.3 


50.7 


45.2 


38.5 


68.6 


58.8 


49.3 


60.4 


52.9 


45.3 


62.1 


51.8 


41.0 



41.2 
30.6 
53.6 
35.1 
43.2 
27.2 
45.8 
34.7 
42.6 
40.6 
30.2 



Table 3. — Mean Temperatures of Selected Stations 
(Compiled from United States Weather Bureau Bui. Q) 
(Degrees Fahrenheit) 



0) 

6 

O 

Q 


03 

3 

a 

03 
i-s 


>> 

M 

03 

3 

M 

.0 

OJ 
pK 


03 


23 


18 


20 


30 


28 


24 


25 


32 


29 


24 


24 


31 


28 


23 


24 


33 


34 


32 


33 


40 


35 


35 


37 


46 


34 


31 


31 


40 


38 


37 


36 


48 


40 


40 


39 


50 


34 


32 


31 


42 


32 


28 


27 


40 


37 


34 


33 


44 


28 


23 


31 


39 


29 


27 


30 


39 


25 


21 


25 


34 


32 


30 


34 


42 


36 


32 


37 


45 


41 


39 


42 


46 


42 


41 


43 


47 


32 


26 


30 


40 


31 


30 


35 


42 


37 


33 


37 


45 


47 


46 


50 


54 


46 


45 


51 


54 


56 


54 


55 


57 


40 


40 


42 


52 


36 


31 


36 


38 









M 




a 

a 

3 

1-5 


>> 
"3 


3 
M 

3 
< 


a 

a 

a 


u 
<u 

-a 
o 
a 
O 


64 


69 


66 


59 


47 


66 


70 


68 


61 


49 


66 


71 


69 


63 


51 


68 


73 


71 


64 


51 


72 


76 


74 


67 


56 


73 


76 


75 


67 


58 


72 


75 


74 


67 


55 


68 


70 


70 


64 


54 


72 


75 


74 


68 


57 


70 


74 


72 


65 


53 


73 


77 


75 


68 


57 


73 


77 


76 


69 


58 


66 


72 


69 


62 


49 


64 


74 


71 


60 


49 


60 


67 


66 


55 


45 


67 


74 


73 


62 


52 


66 


71 


70 


62 


52 


62 


67 


67 


60 


53 


61 


66 


66 


61 


54 


62 


69 


68 


58 


48 


65 


71 


70 


59 


50 


66 


74 


74 


64 


54 


70 


74 


73 


70 


62 


75 


82 


81 


74 


64 


67 


71 


72 


70 


64 


76 


77 


77 


71 


59 


52 


55 


55 


52 


47 



Lewiston, Maine .... 
Fitchburg, Mass. . . . 
Rochester, N. Y.. . . 

Albany, N. Y 

Vineland, N. J 

Charlottesville, Va. . , 
Martinsburg, W. Va. 
Waynesville, N. C. . . 

Clayton, Ga 

Marietta, Ohio 

Griggsville, 111 

Springfield, Mo 

Montrose, Colo 

Provo, Utah 

Missoula, Mont 

Payette, Idaho 

The Dalles, Ore 

Albany, Ore 

Roseburg, Ore 

Spokane, Wash 

Moxee Wells, Wash.. 
Walla Walla, Wash. . 

Sacramento, Cal 

Fresno, Cal 

Los Angeles, Cal. . . . 

Roswell, N. M 

Sitka, Alaska 



628 



FUNDAMENTALS OF FRUIT PRODUCTION 



apDle on June 20. Early Richmond cherries and Champion gooseberries were 
ripe August 15; the Cuthbert raspberry usually ripens during the last of August. 
These dates explain the ability of only a few apple varieties to mature fruit there, 
the most satisfactory being Yellow Transparent and Livland Raspberry. Pat- 
ten Greening has set good crops but failed to ripen its fruit. 

On the other hand, gooseberries, currants and red raspberries thrive at this 
point and bear heavily. At the Kenai Station, where repeated efforts failed to 
produce grain crops because of the cool summers, these fruits were satisfactory. 16 
Evidently then, though these fruits endure less heat and drought than grain 
they endure more rain and low growing season temperatures. Their growing 
season requirements appear to resemble those of cabbage and potatoes. 

Table 4. — Absolute Minimum Temperatures of Selected Stations 

(Compiled from United States Weather Bureau Bui. Q) 

(To 1906, Degrees Fahrenheit) 



October November 



December 


January 


February 


-21 


-24 


-24 


-14 


-14 


-16 


-11 


-12 


-12 


-17 


-24 


-18 


- 5 


-11 


-13 


4 


- 1 


- 9 


- 2 


- 2 


-13 


- 4 


-12 


-10 


2 


- 1 


- 5 


- 4 


- 8 


-22 


-16 


-20 


-22 


-11 


-17 


-29 


-17 


-20 


-13 


- 6 


- 7 


-18 


-23 


-42 


-36 


- 6 


-13 


-15 


-18 


-13 


-19 


18 


10 


11 


7 


- 6 


3 


-18 


-30 


-23 


- 8 


-15 


-22 


- 2 


-17 


-15 


24 


19 


21 


23 


20 


24 


30 


30 


28 


- 3 


- 4 


-14 



March 



Lewiston, Maine. . . . 

Fitchburg, Mass 

Rochester, N. Y 

Albany, N. Y 

Vineland, N. J 

Charlottesville, Va. . . 
Martinsburg, W. Va. 
Waynesville, N. C . 

Clayton, Ga 

Marietta, Ohio 

Griggsville, 111 

Springfield, Mo 

Montrose, Colo 

Provo, Utah 

Missoula, Mont 

Payette, Idaho 

The Dalles, Ore 

Albany, Ore 

Roseburg, Ore 

Spokane, Wash 

Moxee Wells, Wash. . 
Walla Walla, Wash. . 

Sacramento, Cal 

Fresno, Cal 

Los Angeles, Cal 

Roswell, N. M 



18 
22 
19 
23 
22 
26 
23 
16 
24 
19 
20 
21 
19 
12 
7 
16 
20 
29 
22 
12 
13 
24 
36 
36 
40 
19 



2 

5 

1 

10 

14 

15 

15 

9 

14 

15 

2 

6 

-18 

3 

-20 

- 6 

- 2 
23 
14 

-13 
-22 

- 9 
27 
27 
34 
10 



4 

4 

7 

8 

10 

10 

1 

2 

8 

2 

2 

3 

2 

7 

-18 

12 

- 1 

9 

18 

-10 

2 

2 

29 

28 

31 

14 



The Effect of Bodies of Water on Temperature. — Large bodies of 
water have been said to retard temperature changes, making conditions 
in their vicinity rather more favorable for fruit growing. Table 5 
assembles data showing mean monthly temperatures for stations selected 



THE GEOGRAPHY OF FRUIT GROWING 



629 



Table 5. — Monthly Mean Temperatures at Coastal and at Inland Points 

{Compiled from Bigelow 3 ) 
(Degrees Fahrenheit) 





>> 
u 
03 

3 

a 

03 
•"5 


>> 
u 

03 
3 
u 
£> 



u 
03 


O, 

< 


>, 

01 


e 

3 




3 
M 
3 
< 


u 

<u 
X> 

a 

a 

02 


3 

O 
o 
O 


u 

3 

Xl 

B 

o 

>• 

o 


u 

o 

a 

a 

V 

Q 


1. Grand Haven, Mich 

2 Grand Rapids, Mich 


24.5 
23.8 
24.7 
23.0 
19.8 
16.5 
20.1 
15. 1 
26.5 
25.5 
11.4 
18.3 


24.2 
25.5 


30.8 
33 


44.0 
46.2 

42,3 


54.8 
59.0 
54.5 
57.3 
53.6 
57.6 
46.9 
53. 5 
57.3 
58 8 


64.7 
68.1 
65.1 
66.9 
63.5 
67.3 
54.4 
62.7 
67.0 
67.2 
68.8 
69.6 


69.7 
72.6 
70.2 
70.8 
69.7 
72.4 
59.8 
66.6 
71.8 
71.8 
73.5 
74.7 


67.8 
70.0 
68.8 
68.6 
68.7 
69.6 
59.7 
62.9 
69.9 
69.3 
70.7 
72.0 


61.1 
61.8 
62.9 
61.6 
61.5 
61.1 
55.2 
54.6 
63.9 
62.2 
61.7 
63.6 


50.2 
50.1 
51.5 
51.0 
50.2 
48.8 
46.6 
43.6 
53. 1 
51.4 
48.2 
52.0 


38.0 
38.1 
39.3 
38.7 
36.1 
34.2 
36.8 
32.0 
41.1 
39. 1 
33.0 
36.0 


30.1 

28.8 


3 Buffalo, N. Y 


24.0 31.2 


30.1 




23.8 
21.9 
19.6 
21.4 
17.2 
26.1 
26.9 
15.1 
21.6 


31.444.4 
30.9 41.8 


28.3 
26.0 




30.1 
28.9 
26.2 
33.1 
34.9 
28.4 
33.2 


44.5 
38.3 
40.2 
44.7 
47.1 


22.7 


7. Eastport, Maine 

8 Northfield, Vt 


25.3 
20.5 


9 Erie, Pa 


31.7 




29.8 




46.3 59.5 


19.0 


12. Dubuque, Iowa 


48.9 60. 8 


24.5 



to illustrate this influence. With the exception of the Iowa points, the 
stations are arranged in contrasting pairs, the odd-numbered stations 
being located close to considerable bodies of water. In practically every 
case these stations show higher January means and lower July means 
than the respective stations with which they are contrasted. In every 
case the April temperature for the inland station is higher and November 
temperature lower than at the points near water. The Iowa stations of 
approximately the same latitude as the majority of the more eastern 
points show intensification in all these differences. Milwaukee and 
Grand Haven, at almost opposite points on Lake Michigan, show the 
influence of the lake on the prevailing winds blowing over it. That the 
retardation for these stations is generally somewhat greater in the spring 
than in the fall is shown by Table 6. 



Table 6. — Dates When Normal Temperature Crosses 40°F. 
(Compiled from Bigelow 3 ) 

1. Grand Haven, Mich Apr. 7 Nov. 8 

2. Grand Rapids, Mich Apr. 3 Nov. 9 

3. Buffalo, N. Y Apr. 11 Nov. 12 

4. Syracuse, N. Y Apr. 7 Nov. 11 

5. Milwaukee, Wis Apr. 12 Nov. 5 

6. Madison, Wis Apr. 7 Nov. 2 

7. Eastport, Maine Apr. 23 Nov. 5 

8. Northfield, Vt Apr. 16 Oct. 25 

9. Erie, Pa Apr. 5 Nov. 17 

10. Scranton, Pa Mar. 30 Nov. 12 

11. Charles City, Iowa Apr. 4 Nov. 2 

12. Dubuque, Iowa Mar. 31 Nov. 7 



630 FUNDAMENTALS OF FRUIT PRODUCTION 

Attention may be called to some of the northern finger-like extensions 
of the Lower Austral zone into latitudes that for the most part belong in 
the Transition zone. Those along the eastern shore of Lakes Michigan 
and Huron, the southern shores of Lakes Erie and Ontario and the eastern 
shore of Lake Champlain are cases in point and illustrate the extent to 
which climate is tempered and consequently life zones are modified 
through the influence of large bodies of water. Lippincott gives one 
concrete illustration of this influence: 41 On Jan. 1, 1864, a cold wave 
swept over the north central part of the United States. Many Minnesota 
points registered temperatures as low as — 38°F. ; at Milwaukee the 
thermometer went to — 30°F.; yet at Holland, Mich., across Lake Michi- 
gan from Milwaukee — 8°F. was the lowest temperature recorded. 
Further inland, at Lansing, Mich., however, — 22°F. was experienced. 
Peach buds were uninjured in a narrow belt along the eastern shore of the 
lake but were killed at distant points. The data for Milwaukee and 
Grand Haven in Table 5 show that this influence is constant. 

Influence of Altitude on Air and Soil Temperatures. — It is well known 
that an increase in altitude is accompanied by many of the same changes 
as an increase in latitude, the most important being one in temperature. 
It is true also that an increase in altitude is accompanied by certain 
changes in physical environment that are not found at correspondingly 
higher latitudes. Thus Kerner and Oliver report that in the Tyrolese 
Alps at an altitude of 2600 meters the chemical activity of the sun's rays 
is 11 per cent, greater than at sea level. This alone may account for 
some of the peculiarities of plant associations noted at different altitudes 
and possibly may go far toward explaining the more brilliant and intense 
coloring of certain fruits and their better finish at high altitudes. The 
same authors report a different ratio between mean soil and air tempera- 
tures at high as compared with low elevations (see Table 7) and this too 
may either intensify or suppress, as the case may be, the differences 
associated with variations in air temperature only. 

Table 7. — Increase of Mean Soil Temperature Over Mean Air Temperature 
with Increased Altitude in Tyrolese Alps 37 



Elevation, meters 


Excess of mean soil temperature over 
mean air temperature, degrees Centigrade 


1000 
1300 
1600 
1900 
2200 


1.5 
1.7 
2.4 
3.0 
3.6 



THE GEOGRAPHY OF FRUIT GROWING 631 

GEOGRAPHY OF FRUIT PRODUCTION AS INFLUENCED BY RAINFALL AND 

HUMIDITY 

Of hardly less significance than temperature is the influence of humid- 
ity in determining the limits of life and crop zones and in the geography 
of fruit growing. By humidity is meant here total rainfall, distribution 
throughout the season, availability for plant growth and atmospheric 
humidity. Only in countries or districts where the topography leads to 
marked differences in rainfall between points close together and enjoying 
practically the same temperatures are the full effects of humidity strikingly 
brought out. Thus " . . .at one of the substations of the United States 
Experiment Station on the Island of Hawaii, a rainfall of 360 inches was 
recorded for 1 year, while at a point 28 miles away the annual rainfall for 
the same year was 6 inches. It is possible ... in the space of an hour's 
ride to pass from a desert covered with cacti and other drought-resistant 
plants into a dense tropical jungle reeking with moisture." 64 

For the most part fruit trees thrive better in a fairly humid climate, 
a fact shown by the natural distribution of their undomesticated relatives. 
Many species, however, like the date palm and olive, succeed in a very 
arid climate. Some of the great variations in the actual water require- 
ments of different kinds of fruit are shown by data presented in the sec- 
tion on Water Relations. Often different varieties of the same kind 
of fruit vary considerably in water requirements. The Yellow Trans- 
parent apple will thrive and produce good fruit on less water than the 
Winesap or York. Certain varieties or types of dates are grown at 
Alexandria, Egypt, where the mean atmospheric humidity is from 64 to 
72 per cent, while certain other varieties are grown in some of the desert 
oases having an atmospheric humidity of only 34 per cent. Those varie- 
ties that thrive under the one set of conditions, however, cannot be grown 
successfully in the other environment. 43 As these humidity requirements 
of different fruits become known it is possible to draw, more or less accur- 
ately, iso-hyetal lines setting approximate boundaries for districts in 
which they may be expected to reach a high degree of development. 

Data presented in Table 8, however, show the danger in placing too 
much reliance upon rainfall figures as an index to fruit crop or varietal 
adaptation. Thus Fitchburg, Mass. has a mean annual rainfall of 45.4 
inches, 28.6 coming during the growing months, while Missoula, Mont., 
has a total precipitation of only 15.5 inches, of which 10.4 comes during 
the growing months; yet both are apple growing centers and Mcintosh 
is one of the most satisfactory varieties in both places. Irrigation, how- 
ever, is employed in Montana. Vineland, N. J., has an annual rainfall 
of 47.3 inches, three-fourths of which falls during the growing season; 
yet The Dalles, Ore., with less than one-third of that total rainfall and 
with only one-sixth as much falling during the growing season as comes 
during the corresponding period in New Jersey, produces peaches and 



632 



FUNDAMENTALS OF FRUIT PRODUCTION 



other stone fruits with success and without the aid of irrigation. A 
season with a summer rainfall as low as that of The Dalles, would involve 
considerable loss in New Jersey. The summer temperatures of the two 
locations are very much alike, as shown in Table 3. Irrigation is con- 
sidered an absolute necessity in many localities with higher yearly and 
growing season rainfalls than those of The Dalles. The explanation of the 
ability of the Oregon section to produce fruit successfully and with such 
a limited water supply lies in the depth and character of its soil and in the 
methods of soil management employed. The data in this table, however, 
taken in consideration with the methods of culture that are practiced and 
the varieties that are grown in the different sections point out certain 
general limitations that are placed on fruit culture by rainfall and the 
methods that may be employed by fitting practice and variety to varying 
conditions of humidity. 

Table 8. — Mean Rainfall of Selected Stations 

(Compiled Chiefly from United States Weather Bureau Bui. Q) 

(inches) 





C 









03 




<V 








M 













S 







CD 


So 


J2 
















O 


Eh 



Rumford Falls, Maine 

Fitchburg, Mass 

Rochester, N. Y 

Albany, N. Y 

Vineland, N. J 

Martinsburg, W. Va. . 
Charlottesville, Va. . . . 
Waynesville, N. C. . . . 

Clayton, Ga 

Marietta, O 

Griggsville, 111 

Springfield, Mo 

Montrose, Colo 

Provo, Utah 

Missoula, Mont 

Payette, Idaho 

The Dalles, Ore 

Albany, Ore 

Roseburg, Ore 

Spokane, Wash 

Moxee Wells, Wash... 
Walla Walla, Wash. . . 

Sacramento, Cal 

Fresno, Cal 

Los Angeles, Cal 

Roswell, N. M 

Sitka, Alaska 

Lincoln, Neb 



4. 1 


3.0 


4.0 


3.3 


3. 1 


2.4 


2.8 


2.4 


4.3 


3.3 


3.1 


3.2 


3.6 


3.4 


6.4 


4. 1 


7.8 


6.3 


3.2 


3.3 


3.2 


3.3 


3.9 


3.8 


0.8 


1.0 


1.3 


1. 1 


1.0 


1.0 


0.9 


1.0 


1.3 


0.7 


4.7 


3.6 


3.7 


2.5 


1.4 


1.3 


0.5 


0.6 


1.7 


1.8 


2.8 


2.0 


1.5 


0.6 


2.7 


1. 1 


0.2 


0.4 


5.8 


6.3 


1.3 


2.8 



7 
6 


7 
2 
1 
7 
2 
(I 
3 
!) 

7 
5 
2.2 
1.4 
0.6 
2.6 
2.0 
1.4 
0.9 
1.7 
1.0 
0.5 
0.5 
1.2 
3.5 
4.3 



3.8 


4.5 


3.0 


2.9 


3.1 


3. 1 


3.7 


3.9 


3.6 


4.6 


3.6 


3.7 


5.5 


5.7 


4.4 


4.6 


5.3 


7.0 


4.5 


4.4 


4.5 


3.7 


4.8 


4.2 


0.2 


0.8 


0.5 


0.2 


2.1 


1.0 


0.6 


0.4 


0.6 


0. 1 


1.3 


0.3 


1.2 


0.4 


1.5 


0.7 


0.4 


0. 1 


1. 1 


0.4 


0.2 


T 


0. 1 


T 


0.1 


T 


2.0 


3.4 


2.8 


4.2 


4.3 


3.8 



3.2 

4.4 
2.9 
4.0 
4.8 
3.2 
5.0 
4.5 
7.2 
3.9 
2.7 
3.9 
1.2 
0.2 
0.7 
0.3 
0.2 
0.4 
0.4 
0.5 
0.2 
0.4 
T 
T 
T 
2.2 
6.7 
3.7 



3.0 
3.4 
2.3 
3.2 
3.8 
2.5 
5.2 
2.4 
4.9 
3.0 
4.0 
3.8 
1.0 
0.4 
1.2 
0.5 
0.6 
2.0 



1.0 
0.3 
0.3 

0.8 

2.0 

10.7 

2.6 



3.0 


28.3 


4.0 


28.6 


2.8 


22.7 


3.1 


26. 1 


3.6 


31.7 


1.6 


25. 1 


3.5 


37.0 


2. 1 


32.2 


4.0 


45.7 


2.9 


29.2 


1.9 


28.6 


2.9 


33.2 


0.8 


6.5 


0.8 


6.0 


1.2 


10.4 


1.0 


6.1 


1.3 


5.4 


3.4 


18.3 


2.6 


13.9 


1.4 


9.2 


0.5 


3.6 


1.5 


9.6 


1. 1 


7.4 


0.6 


3.6 


1.5 


6.7 


1.6 


13.0 


12. 1 


52. 1 


1.8 


24.6 



42.1 
45.4 
34.5 
36.9 
47.3 
35.2 
49.8 
47.7 
68.5 
42.1 
37.0 
43.6 

9.3 
10. 
15. 
12. 
15. 
44. 
34.9 
18.3 

8.9 
17.7 
19.9 

9.2 
15.6 
15.6 
82.3 
27.5 



THE GEOGRAPHY OF FRUIT GROWING 



633 



OTHER FACTORS INFLUENCING THE GEOGRAPHIC DISTRIBUTION OF 

FRUITS 

Sunshine. — The amount of sunshine to which the trees are exposed 
during their growing season is perhaps of secondary importance in deter- 
mining the character of the fruit industry that may develop in different 
sections, since it nowhere becomes so reduced as to be permanently a limit- 
ing factor. However it is often decisive in determining the varieties that 
can be grown to advantage. This is true at least in the apple in which 
coloration depends directly on the relative amount of sunshine that reaches 
the fruit during the ripening season. Thus the data in Table 9 suggest 
why it is practicable to grow varieties like Winesap at Grand Junction, 
Col. and in eastern Washington, but not in the vicinity of Portland, 
Ore. 

Table 9. — Hours of Sunshine for Selected Stations 
(Compiled from United States Weather Bureau Bui. Q) 



March 


April 


May 


June 


July 


August 


195 


213 


258 


274 


276 


258 


186 


240 


279 


300 


279 


248 


171 


225 


266 


290 


296 


258 


152 


221 


263 


287 


318 


269 


198 


250 


284 


293 


299 


271 


197 


255 


312 


303 


274 


253 


178 


236 


244 


275 


312 


256 


199 


240 


267 


295 


341 


290 


192 


204 


232 


261 


291 


279 


128 


181 


224 


240 


279 


240 


196 


222 


294 


354 


405 


354 


193 


236 


288 


355 


370 


329 


252 


279 


337 


369 


370 


317 


194 


235 


286 


330 


372 


310 


166 


200 


230 


329 


268 


183 


241 


324 


370 


404 


429 


400 


255 


275 


259 


289 


341 


328 



September 



October 



Boston, Mass 

Albany, N. Y 

Rochester, N. Y 

Erie, Pa 

Raleigh, N. C 

Atlanta, Ga 

St. Paul, Minn 

Omaha, Neb 

Kansas City, Mo 

Parkersburg, W. Va.. . 

Boise, Idaho 

Salt Lake City, Utah.. 
Grand Junction, Col.. 

Spokane, Wash 

Portland, Ore 

Fresno, Cal 

Los Angeles, Cal 



232 
240 
223 
213 
271 
250 
235 
250 
252 
199 
298 
296 
312 
226 
148 
336 
282 



185 
186 
158 
157 
220 
235 
176 
202 
236 
159 
216 
236 
265 
160 
64 
290 
263 



Parasites. — The prevalence of certain parasites is another factor of no 
mean importance in determining the geographic distribution of fruit 
growing — at least in determining what kinds of fruit shall be grown 
in different districts. For instance, European grapes are not grown in 
the southeastern United States on account of the prevalence there of the 
grapevine phylloxera and the downy mildew. European plums are 
commercially unimportant in the Middle West on account of the brown 
rot and the black knot. Perhaps in the last analysis certain insects and 
diseases are particularly troublesome in certain districts because they 
find there temperature and humidity conditions that are especially favor- 
able for their development and spread ; hence fundamentally it is temper- 
ature or humidity that really sets limits for these fruits. Nevertheless 



634 FUNDAMENTALS OF FRUIT PRODUCTION 

the immediate factor responsible for limitation of the industry is a 
parasite. 

Wind. — Wind is often considered important in determining whether 
fruits can or cannot be grown successfully in certain sections. It is to 
be doubted if wind alone is of great significance over any wide areas. On 
the other hand, extreme heat or dryness accompanied by winds may 
cause much damage and practically prevent the culture of certain fruits 
in large areas where they frequently occur. Actually in such cases it is 
the combination of high temperature or low humidity — or both — with the 
wind that is the real factor. 

Native Range of Parent Species. — The native range of the parent 
species without doubt furnishes some indication of the probable geo- 
graphic range of the forms that are brought under cultivation ; neverthe- 
less it is doubtful if it is an index with most fruits of the extent to which 
they may be grown for commercial production. For instance, the com- 
mon European plum (Prunus domestica) is native to central and south- 
eastern Europe. Its cultivation extends to practically all of Europe 
and to much of temperate North America and it is grown to a limited 
extent in many other parts of the world. Though the native home 
of the peach is supposed to be China, it reaches its greatest commercial 
importance in Europe, North America and southern Africa. The 
Evergreen blackberry (Rubus laciniatus) apparently is not cultivated in 
southwestern Europe where it is found wild, but is of considerable impor- 
tance in the Pacific Northwest 6,000 miles from its native home. On 
the other hand the culture of the North American plum (Prunus ameri- 
cana) is restricted to an area considerably less than the native range of 
the parent species and the litchi (Nephelium litchi) is not grown com- 
mercially outside China. 

Length of Time in Cultivation. — The length of time a species has been 
under cultivation naturally has some influence on the amount of territory 
over which it extents. Fruits of recent introduction, such as the pecan, 
the blueberry and the loganberry have not had time to become dissemin- 
ated widely and tried thoroughly in many sections. On the other hand, 
though the Chinese jujube probably has been in cultivation as long as 
the peach, its present geographic range is very small as compared with 
that of its sister fruit coming from the same general region. Some 
species, such as the fox grape (Vitis labrusca), are cultivated over a very 
wide range of territory though they have been in cultivation only a few 
decades. 

Uses and Quality of Product. — The variety of uses that the fruit and 
the plant producing it serves has been doubtless an important factor in 
making the cocoanut palm one of the most widely distributed fruits in 
cultivation. For many tropical peoples it is the one most important 
plant and there has thus been every encouragement to disseminate it 



THE GEOGRAPHY OF FRUIT GROWING 635 

widely. The same may be said of the banana. On the other hand, 
though the date palm and the fig are hardly less important, their actual 
cultural range is much more restricted. 

Quality of product is certainly relatively unimportant in determining 
geographic distribution. Best evidence on this point is obtained by a 
comparison of varieties within a group, for it is hardly fair to compare the 
quality of one group, for example the orange, with that of another, for 
example the raspberry. Though Elberta is admittedly a second rate 
peach in quality, it dominates the peach industry of America. The 
Kieffer pear and the Ben Davis apple occupy similar, though perhaps not 
quite so prominent, positions in their respective groups. 

Relation to Consuming Centers and Transportation Facilities. — The 
location of large consuming centers and their relation to efficient systems 
of transportation is very important in determining where many fruits, 
particularly those of a more perishable character, are grown in quantity. 
For instance a map showing the distribution of the strawberry industry 
of North America indicates production centers close to nearly all the 
larger markets; those production centers distantly located from large 
markets are connected with them by good transportation systems. 
The same statements hold for raspberry, blackberry and dewberry pro- 
duction and to a certain extent for fruits like the peach, cherry and plum. 
However, many centers of heavy production of these fruits are not par- 
ticularly well located from the standpoint of nearby markets or quick 
and cheap transportation. Almost invariably the presence of fruit 
product plants of one kind or another makes possible the location of the 
industry. Were it not that a comparatively large percentage of the 
world's grape crop has been utilized for wine making for thousands of 
years, it might be said that fruit product facilities are becoming of 
increasing importance in determining the location of fruit production 
centers. 

Sometimes factors that are more or less artificial operate, at least for a 
time, in determining the development of large fruit industries. For in- 
stance a large fruit product establishment may be located at some point — 
its exact location being determined largely by considerations quite dis- 
tinct from those concerned with fruit production. Within a short time 
a large fruit industry develops in the vicinity of this plant to supply it 
with fresh fruit. Had this plant been located a hundred miles away, the 
first place would have raised no fruit commercially but the industry would 
have developed around the other. It often happens that a pioneer 
in some branch of horticulture makes a marked success of growing some 
particular kind of fruit. His neighbors promptly follow him in the busi- 
ness and soon a whole community or a whole section becomes famous for 
its Cuthbert raspberries, or Mcintosh apples, or Evergreen blackberries 
or Neunan strawberries. In the long run, however, a specialized indus- 



636 FUNDAMENTALS OF FRUIT PRODUCTION 

try develops and remains chiefly in those sections or districts where fac- 
tors governing production, harvesting, distribution and marketing are 
most favorable. In other words, the present geographic distribution of 
the different fruit industries represents the result of a struggle for 
existence, a real natural selection. 

Summary. — The most important environmental factor determining 
the geographic range of cultivated fruits is temperature, though rainfall 
and humidity act as important limiting factors within the wider limits set 
by temperature. The boundary lines of fruit zones follow rather closely 
those of the life zones established by the biologist. Apparently, mini- 
mum winter temperatures are most important in setting the northern 
limits (in the Northern Hemisphere) to the geographic range of species 
and varieties and mean summer temperature during the hottest 6 weeks 
in setting their southern bounds. The limiting effects of natural rainfall 
are often alleviated by the use of irrigation water or by other cultural 
practices and also by the selection of drought resistant varieties. Sun- 
shine, wind and the presence of certain parasites are often important 
factors in determining the range of particular varieties. There is no 
very close relation between the length of time a species or variety has been 
in cultivation or between the natural range of related forms and its 
range in cultivation. Artificial factors, such as nearness to large centers 
of population, transportation and storage facilities, and temporary 
market demands, often are of considerable importance in determining the 
approximate range of a variety or of a fruit and in determining its 
elative importance within different portions of its range. 



CHAPTER XXXIV 
ORCHARD LOCATIONS AND SITES 

The production of fruit on a scale sufficient to meet the needs of the 
home at least partly has a general appeal. Indeed it is exceptional to find 
the farm or even the suburban lot that is without trace of fruit tree, 
shrub or vine. Such planting of a few fruit-producing plants is often done 
as much for the pleasure derived from their culture as for the monetary 
returns. On the other hand, commercial fruit production is a business 
and appeals to only a comparatively small percentage of the popula- 
tion — even of the farming population. Perhaps this is because it is 
generally considered an exacting business, requiring special training or 
special aptitude, or perhaps it is due to other reasons. Whatever the 
reason, the commercial fruit growers are few in comparison with other 
classes of farmers. Nevertheless there are frequent recurring waves of 
interest in commercial fruit production, bringing to those already engaged 
in some line of farming the question whether or not it would be desirable 
for them to set a part of their acreage to fruit, or raising in the minds 
of those who are not engaged in agriculture the question whether they 
might not raise fruit with profit. In either case a number of matters 
concerning the establishment of an orchard should be considered before 
any definite decision is made. These questions are much the same 
fundamentally for the one group of prospective growers as for the other, 
though the points of view may be somewhat different. In the one case 
the problem is to determine what fruits can be grown to best advantage 
in some particular field, farm or locality; in the other it may take the 
form of first deciding on what kinds to grow and then in finding the proper 
place to grow them. 

Orcharding In or Outside of an Established Fruit Growing Section. — 
Incidental to the discussion of the geography of fruit growing some of the 
factors influencing the choice of a location for certain fruits or of fruits 
for certain locations are mentioned. An intelligent selection in either 
case depends on a detailed knowledge of the geographic distribution of the 
industries concerned. Obviously there would be considerable risk in the 
commercial culture of some fruit in a section where it is not being grown — 
where it has never been tried or where its cultivation has been discon- 
tinued. Thus it would not seem wise to attempt commercial filbert 
culture in New York or Pennsylvania, or to make other than experimental 
plantings of the jaboticaba in southern Florida. It would be safer 

637 



638 FUNDAMENTALS OF FRUIT PRODUCTION 

to undertake the commercial production of any fruit where an industry in 
that particular fruit is already established. 

One great advantage in producing fruit of a kind that is well and 
favorably known and in a section where it is extensively grown is that 
the marketing problem usually presents fewer difficulties. The reputa- 
tion attracts buyers and the fact that growers have been established there 
often means that efficient selling organizations have been formed. How- 
ever, such marketing advantages are often over-emphasized. In years 
of heavy production, the apple grower in western New York may wish 
his orchard were in Indiana or Nebraska. Moreover, land prices are 
likely to be high in sections with established reputations; this means a 
permanently large overhead charge in the cost of production. If fruit 
is to be grown under these conditions, the choice of kinds and varieties 
and the methods of culture must be such as will yield large returns. 
The usual advantages of production where little fruit is raised are cheap 
land and good local markets. However, isolation may mean difficulty 
in getting in contact with buyers, trouble in securing supplies and no 
possibility of cooperative effort. Probably much would depend on 
the scale of operations contemplated. The small grower can often 
produce to better advantage in the less developed sections, though 
conditions favorable to developing a large enterprise are more likely 
to be found where an industry of some size is already established. 

Land Values. — Among the important factors determining the desir- 
ability of a piece of land for fruit growing are : land values, the availability 
of transportation and storage facilities, of fruit products establishments, 
of labor supply, the social conditions and the educational advantages. 
Locations only a few miles apart may vary greatly in respect to one or all 
of these factors. 

Perhaps the price paid for land or its valuation has nothing to do 
with the grade or quantity of fruit that can be produced on a given area 
and the question of conditions favorable for production can possibly be 
considered entirely aside from it. Nevertheless it should be realized 
that successful orcharding is a question not only of production, but 
even more of economical production. This means that there must be a 
reasonably large margin between production costs and selling prices. 
Both production costs and selling prices for fruit fluctuate from year to 
year and the difference between them will likewise vary, but interest on 
investment constitutes a fixed and important part of the overhead charges 
figured into the cost of production. This charge must be discounted 
every year, crop or no crop. For instance, if the orchard at bearing age 
represents an investment of $300 per acre and it yields an average crop 
of 300 bushels per acre the interest charge against each bushel is about 
6 cents; if, however, the orchard represents an investment of $1,000 per 
acre, a crop of the same size would represent an interest charge of 20 



ORCHARD LOCATIONS AND SITES 639 

cents per bushel. Of course, if a bumper crop were harvested in the 
latter case — a crop say of 600 bushels per acre — the interest charge per 
bushel would be only 10 cents; but on the other hand if a light crop, say 
100 bushels, is harvested, the interest charge per bushel would be 60 
cents. It is not the intent here to recommend cheap land for growing 
fruit; such land may prove the most expensive in the end. On the other 
hand the purchaser or owner of high priced land should figure out before 
planting the probable charges per bushel, pound, barrel or other unit of 
fruit produced, that the cost of land contributes toward cost of 
production. 

Transportation Facilities. — The importance of the distance between 
the orchard and the shipping point or the market depends on the character 
of the roads and the value and nature of the crop. Of course the ideal 
location is adjacent to a railroad or other transportation system so that 
there may be facilities for loading at the orchard. Since this is seldom 
possible, access to a loading point must be considered. Six or eight 
miles of ordinary country road has been considered about the longest 
haul practicable with most fruits. If the distance to the shipping point 
is much greater, the item of hauling becomes too large a part of the total 
cost of production and unduly reduces the margin of profit, or possibly 
turns profit into loss. The cost per mile of hauling barreled apples over 
average country roads should not exceed 2 to 3 per cent of the average 
price received for them. Let the distance be such that 10 to 15 per cent 
of the selling price is required to cover this item and it becomes very 
important. The character of the fruit also must be considered. Obvi- 
ously it is impracticable to haul strawberries or other soft fruits as far 
or over as difficult roads as winter apples may be. The better the 
road, however, the greater the distance the crop may be hauled with- 
out injury. A trip of 12 to 15 miles over well graded and smooth sur- 
faced roads may cause much less injury than one or two miles over 
a poor country road. Finally the value of the crop per load is important. 
Thus it may be entirely practicable to plant an English walnut, prune 
or chestnut orchard 10 to 15 miles from a shipping point, for one load 
would carry the crop from 2 acres, while a corresponding area of apple 
orchard would require 10 to 20 two-horse load trips. Furthermore a 
nut crop is not subject to the mechanical injury which would result 
from hauling apples long distances. 

SLOPE OR ASPECT 

Many advantages have been claimed for certain slopes — advantages 
so great that prospective fruit growers are sometimes led to believe that 
success is practically guaranteed if the land but slopes in a certain direc- 
tion and that failure is almost equally certain if it slopes the opposite 



640 FUNDAMENTALS OF FRUIT PRODUCTION 

way. Southern are generally warmer and earlier than northern slopes 
because they receive the more direct rays of the sun. Shreve, 51 who 
has studied the effect of varying physical environment on vegetation 
in mountain regions, summarizes some of the more important influences 
as follows: "Two slopes of the same inclination, which lie in opposed 
positions so that one faces north and the other south, will present to 
plants two environments differing in almost every essential physical 
feature. The temperature of the air on two such slopes might be identical 
as determined by the thermometer of a carefully established meteoro- 
logical station, but they are distinctly different as they affect vegetation, 
for the plants receive very different amounts of heat through diurnal 
terrestrial radiation. This circumstance is of small importance to full- 
grown trees and large plants, but is of great importance to young plants 
and seedlings. The soil temperatures of opposed slopes are also widely 
unlike, even in the presence of the undisturbed cover of natural vegeta- 
tion. The two opposed slopes would in all likelihood receive the same 
rainfall, although this is not necessarily the case. An equal amount of 
rain might effect an equal elevation of the soil moisture on the two slopes, 
and to the same depth, but the soil evaporation of the south slope would 
greatly exceed that of the north slope, and a lower moisture would soon 
prevail in the soil of the former. Greater or less differences may thus 
be shown to obtain between the opposed slopes with respect to the most 
vital features of plant environment. " 

Influence on Soil Temperatures and on the Plant. — Table 10 affords a 
quantitative expression of the influence of slope on mean soil tempera- 
ture. Even more significant are the differences in the temperatures of 
the plants themselves on different slopes. Table 11 shows the mean 
temperatures one inch beneath the surface of the bark on the north and 
south sides of tree trunks at the summit of a hill and on its north and 
south slopes during the winter months in Wisconsin. As would be 

Table 10. — Mean Soil Temperatures (Centigrade) at a Depth of 80 Centi- 
meters for 3 Years on Different Slopes of an Isolated Conical 
Sandhill at Innsbruck, Tyrol 
(After Kerner and Oliver 31 ) 
N. N.E. E. S. E. S. S.W. W. N.W. 

15.3° 17.0° 18.7° 20.0° 19.3° 18.3° 18.5° 15.0° 

expected, the trees on the south slope show higher midday and afternoon 
temperatures than those on the northern slope. They also show rather 
surprisingly lower early morning temperatures. This means that they 
are exposed to greater extremes and more rapid temperature changes. 
The relation of such conditions to certain forms of winter injury is pointed 
out in the section on Temperature Relations. The tendency of the 
north side of the trunk on the north slope to be colder than the south side 
in the early morning while on the south slope the reverse condition holds 



ORCHARD LOCATIONS AND SITES 



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41 



642 FUNDAMENTALS OF FRUIT PRODUCTION 

is due probably to the stronger radiation of heat from the ground on the 
uphill side against the trunk. 

Specific Influence on Fruit Growing. — These data indicate that south- 
ern and eastern slopes are preferable for the production of fruits for the 
early markets or for any fruit or variety with which hastened maturity 
is an important consideration. Thus in New England there are many 
locations where certain varieties of grapes can be ripened properly only 
when grown in sheltered spots with a southern exposure. Often there 
is a difference of a week or more in the maturing seasons of the same 
variety on the northern and southern sides of the same hill, equivalent 
to a location many miles southward or northward. On the other hand 
northern and western slopes are preferable when delayed maturity is the 
object. Fruits of certain species like the apple and peach are likely to 
be somewhat higher colored on southern than on northern slopes. It 
should be noted that late spring and early fall frosts are no more likely 
to occur on one slope than on another and that consequently more 
trouble from spring frosts at least will be encountered on southern than 
on northern slopes because vegetation starts earlier on the former. It is 
probably on this account mainly that, for general fruit growing, a northern 
exposure is preferred by most growers. Areas with eastern and western 
exposures are intermediate in the qualities mentioned between those with 
northern and southern exposures. Western and southwestern slopes 
are perhaps least desirable under average conditions and with most fruits 
because of the action of the sun and of temperature in causing sunscald 
on the west and southwest sides of the trunk. 

Without doubt too much importance is attached by many to the 
advantages or disadvantages offered by particular exposures — at least as 
these exposures have a direct bearing on tree and fruit through a 
modification of temperature and light conditions. In the great majority 
of cases the grower can raise fruit successfully on any and all slopes, pro- 
vided they are not unreasonably steep and have suitable soils. It may be, 
and often is, desirable to plant certain slopes with fruits of one kind or one 
variety and other slopes with other kinds or other varieties, so that the ad- 
vantages offered by the different exposures may be fully utilized. Thus 
early strawberries might be grown on the south and east sides of a hill 
and midseason and late varieties on its west and north sides and the har- 
vesting season thereby lengthened a week at each end. The idea that 
one slope is always best for a certain fruit or a certain variety is erroneous. 
Much depends on where and for what special purpose that variety is 
grown. 

Indirect Effects. — There are certain indirect influences of slope or 
exposure on the growth of trees and their maturing of a crop that are of 
importance equal to, or greater than, that of the more direct influences. 
Southern and western slopes dry out more rapidly and are more subject 



ORCHARD LOCATIONS AND SITES 643 

to drought than others. Fruit grown on northern or eastern slopes 
therefore tends to average somewhat larger in size than that produced 
on a southern or western exposure. In some sections the soil on many 
southern slopes is much thinner than that on northern, eastern or western 
exposures and in such instances a particular slope is to be avoided, not 
because of the slope itself but because of the factors with which it is asso- 
ciated. In much the same way certain slopes are to be avoided in certain 
sections because of their exposure to prevailing winds. When land slopes 
away from the direction of the prevailing wind considerable protection 
is afforded the trees by the contour of the ground, but when it slopes in 
the direction of the prevailing wind much more trouble is likely. 

Abruptness of Slope. — Gentle slopes are almost always preferable to 
abrupt slopes. Many orchards on very steep hillsides have proved 
profitable, but the cost of production under such conditions is likely to 
be considerably higher than on more nearly level land of the same char- 
acter. This of course assumes equally good soil and other conditions on 
the steep and the gentle slopes. Different environmental conditions in 
the two locations may reverse the situation. Thus, in the Piedmont 
section of Virginia where the orchards are planted on steep hillsides and 
where it is necessary to spray five to seven times, apples are produced at 
a lower cost than in the Shenandoah valley where less spraying is required. 
As a rule it is best to limit orchard planting to slopes so gradual that cul- 
tivation may be practiced without great danger from erosion and over 
which spraying machinery and other equipment may be hauled without 
serious difficulty. The necessity of gentle slopes is still greater in sections 
where irrigation is practiced. 

AIR DRAINAGE 

Fruit growing, more than almost any other branch of agriculture, 
requires comparative freedom from untimely late spring and early fall 
frosts; in turn the occurrence of frosts within certain limits is determined 
largely by what is commonly known as "air drainage," the settling of 
cold air to lower levels. This is discussed in some detail in the section on 
Temperature Relations. 

Influence of Elevation. — Many factors influence air drainage, some 
to a very marked extent and others only to a comparatively small degree. 
Probably the most important single factor in air drainage is elevation. 
Height above adjoining land or fields usually is of greater significance 
than absolute elevation above sea level. Frost is as likely to occur during 
the danger period at the high elevations found in some of the intermoun- 
tain fruit growing districts as at the low elevations of the seaboard. 
Portions of the Ozarks with an elevation of over 1,000 feet are as frosty 
as the Hudson River valley, which lies only a little above sea level. 



644 



FUNDAMENTALS OF FRUIT PRODUCTION 



However, as a rule, low lying land is more subject to frost than that 
somewhat elevated above surrounding or adjoining fields, though there 
are certain exceptions which are discussed later. 

The difference in temperature between two points, one of which is 
50 or 100 feet above the other, of course depends on many factors, such 
as general lay of land, relative areas of the land having the respective 
elevations and proximity to bodies of water. However, the inequality 
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at different heights above the base of a steep hillside, showing the great differences in 
temperature that sometimes develop on a clear, still night. Although the temperature at 
the base was low enough to cause considerable damage to fruit, the lowest temperature 
225 feet above on the slope was only 51°F. Note that the duration of the lowest tempera- 
ture was much shorter on the hillside than at the base. (After Batchelor and West 2 ) 

there is greatest danger from frost, between points only a few dozen feet 
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ure 67 shows graphically the diversity in minimum temperature that 
sometimes occurs with variations in elevation of 25, 50 and 225 feet. 
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by a difference of approximately 5°F. between 8:00 p.m. and 8:00 a.m. 
and an inequality of 50 feet was accompanied by a variation of 15° 
to 20°F. At greater elevations the temperature was still higher, though 
its rise was not proportional to the increase in height. 

This suggests that extreme divergencies in altitude, therefore, are 
likely to afford much greater security from frost than moderate differences, 
very slight inequalities, even of only a few feet, often are associated with 
a sufficient variance in temperature to result in crop safety or crop loss. 
Perhaps more nearly average differences in minimum temperature due 



ORCHARD LOCATIONS AND SITES 



645 



to elevation are shown in Fig. 68. These graphs represent temperature 
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valley during the blossoming period of fruits. Though the minimum 
temperature was not invariably recorded at the lowest elevations, on 
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| 9 , 4 10, 28 5 1 9 12 13 14 16 11 19 20 22 23 24 25 2& 27 
April May 

Fig. 68. — The daily minimum temperatures for stations of different elevations extend- 
ing from the high agricultural land to the lowest agricultural land of the valley. (After 
Batchelor and West 2 ) 

elevations registered temperatures above the probable danger point 
and a fruit crop on the lower levels probably would have been destroyed. 
"The minimum temperatures experienced by the bench lands and upper 
slopes of the tillable area in a mountain valley average from 6 to 10°F. 
warmer than the valley bottoms due to the drainage of cold air to the 
low areas during the typical clear, calm, frosty nights." 2 On calm but 
cloudy nights the variation in minimum temperatures between high 
and low points in this valley is reduced to about 40 per cent, of that 
on calm, clear nights and during windy weather there is very little differ- 
ence in their minimum temperatures. 



646 FUNDAMENTALS OF FRUIT PRODUCTION 

The point should be emphasized that the amount of air drainage 
secured by selecting a site somewhat above the adjoining fields depends 
not alone on the amount of elevation, but also on the area from which 
the cold air drains in comparison with the extent of that to which it 
may settle. If the low ground upon which the cold air may sink is 
limited in extent and has little outlet while the area to be drained is 
large, this depression will soon be filled with cold air and the slope above 
will be afforded no further protection. The case is comparable with a 
large watershed supplied with an inadequate drainage system. An 
elevation of 20 or 25 feet above a wide valley may thus afford better 
air drainage for one orchard than an elevation of 50 feet above a narrow 
valley affords another. In many cases a ravine or narrow draw along one 
side of an orchard will afford a given site better air drainage than an 
adjoining low-lying field covering many acres, provided the draw or 
ravine is deep, has a good outlet and is not clogged with brush and timber 
that interferes with free movement of the air. In other words, of 
two areas having the same elevation one may enjoy much better air 
drainage and greater freedom from frost because of differences in the 
contour and topography of the land that borders them. 

The graphs in Fig. 68 show the maximum variations in temperatures 
during the night between stations at different elevations on a hillside. 
Though day temperatures are not given there is the suggestion that 
they approximate rather closely. Available data show that such in- 
equalities in elevation as are normally found within single fruit growing 
districts are responsible for but small differences in maximum day 
temperatures. 2 In other words, elevation materially influences minimum 
and average, but not maximum, temperatures. 

Thermal Belts. — The influence of elevation on air drainage and 
consequently on the selection of sites for fruit growing should not be 
passed over without a reference to the so-called "thermal belts," "ther- 
mal zones," "frostless belts" or "verdant zones," as they are variously 
called . They are comparatively frost-free belts along hillsides or mountain 
ranges, below and above which frost occurrence is not uncommon. The 
limits of comparatively few such zones have been accurately mapped; 
consequently the fruit industry has developed more or less independently 
of them. However, their occurrence presents an interesting phenomenon 
and it is desirable to recognize and if possible, make use of the obvious 
advantages they provide, for without doubt the fruit growing districts 
of the country include many such zones that are not being utilized for 
fruit production. 

The following quotations from an article by Abbe 1 will point out 
more exactly the conditions characteristic of thermal belts: 

"Prof. J. W. Chickering, Jr., in the Bulletin of the Philosophical Society of 
Washington, March, 1883, and in the American Meteorological Journal, Vol. I, 



ORCHARD LOCATIONS AND SITES 647 

describes the following thermal belt: 'In Polk County, North Carolina, along 
the eastern slope of the Tryon Mountain range, in latitude north 35°, the thermal 
belt begins at the base of the mountain, at an elevation of 1200 feet. It is 
about 8 miles long, and is distinguished by magnificent flora, such as would be 
characteristic of a point 3° south of the actual latitude.' 

"Prof. John Leconte, of Berkeley, California, in Science, Vol. I, p. 278, states 
that at Flat Rock, near Hendersonville, Henderson County, North Carolina, on 
the flank of the mountain spur adjacent to the valleys of the Blue Ridge, he also 
observed a frostless zone. The valley is about 2200 feet above sea level, and 
the thermal belt is 200 to 300 feet above the valley. 

"J. W. Pike, of Vineland, N. J., states that among the mountains of 
California he has discovered that during the night the cold is much greater in 
the valleys than on the terraces several hundred feet above, due to the settling 
of the cold air, so that a thermal belt is formed at that height separating the 
frosty valleys from the colder highlands. 

"In the Tennessee Journal of Meteorology for January, 1894, published by the 
State Weather Service, the author describes a thermal belt between Los Angeles 
and the Pacific Coast. It traverses the foothills of the Cahuenga range, and 
has an elevation of between 200 and 400 feet and a breadth of about 3 miles. 
It occupies the midway region of the range. 

"In the American Meteorological Journal, Vol. I, S. Alexander describes 
a thermal belt in which the peach tree flourishes in the southeastern portion of 
Michigan. He shows that the cold island discovered by Winchell in that region 
is really the bottom of a topographical depression into which the cold air settles. 
It is a long valley surrounded by a belt of elevated country from 50 to 600 feet 
above Lakes Michigan and Huron. The valley and the isotherms trend north- 
east and southwest from Huron County through Sanilac, Lapeer, Oakland, Liv- 
ingston, and Washtenaw to Hillsdale Counties. The highlands of this region 
are all much freer from frost than the lowlands, and all much more favorable for 
early vegetation. He does not state that any point is high enough to be above 
the thermal belt, but that, in general, two equal parallel thermal belts inclose the 
cold island between them. 

"It is generally conceded that these thermal belts depend both upon the 
drainage of cold air downward into the lower valleys and the freedom of radiation 
from the surface of the ground to the clear sky overhead. During a still night, 
when frosts occur, the surface of the hillside cools by radiation, and hence cools 
the air in contact with it; the latter flows downward as long as its cooling by 
radiation and conduction exceeds its warming by compression. Inasmuch as its 
cooling depends on contact with a still colder soil or plant, it soon accumulates 
in the lowlands as a layer of cold air, which grows thicker during the night by 
the steady addition of the thin layer of descending air in contact with the ground 
on the hillsides. The warmer air, which has not yet had an opportunity to cool 
by contact with the ground, floats on top of the cold mass; it spreads out toward 
the hills, and is continuously furnishing its heat to the adjacent hillsides as fast 
as it comes in contact with them before it also cools and descends. The formation 
of the thermal belt seems to depend largely upon this gentle circulation during 
the night time. The lower limit of the belt is defined by the depth of the accumu- 
lation of cold air io the confined valley and rises higher in proportion as the night 



648 FUNDAMENTALS OF FRUIT PRODUCTION 

is clearer and longer, and also In proportion as the valley is more or less perfectly 
inclosed. The upper limit of the thermal belt may depend upon the strength of 
the wind, and the general temperature of the air. But if there be no wind, then 
it depends equally on the freedom of radiation to the clear sky and on the above- 
described circulation of air." 

Influence of Bodies of Water. — After elevation, probably the next 
most important factor influencing air temperature and drainage is 
proximity to bodies of water. The specific heat of water is high; it 
absorbs heat slowly and gives it up slowly. Consequently in the spring 
a large body of water warms more slowly and in the fall it cools more 
slowly than the surface of the adjacent land or than near by vegetation. 
It is slower even than the atmosphere in responding to changes in tem- 
perature. Relatively the air shows a great variation in temperature 
between night and day, while a body of water of considerable size shows 
no appreciable change. The air warmed during the day, coming in 
contact with the surface of a body of water, is cooled; consequently the 
air in close proximity to such a body is cooler than it would be otherwise. 
On the other hand, at night air cooled to a temperature below that of 
the water, is warmed by contact with its surface and in turn gives up 
that heat to vegetation and other bodies with which it comes in contact. 
Consequently points close to bodies of water are frequently somewhat 
cooler during the day and warmer at night than corresponding inland 
points and are freer from frosts, while blossoming is at the same time 
retarded in their proximity. 

Influence of Distance from Water. — Some measure of this influence 
may be obtained from data presented in Table 12 showing the air tem- 
peratures, atmospheric humidity and dewpoints for three stations in 
New Jersey and one on Kelley's Island in Lake Erie for the months of 
July and August, 1866. Vineland is about 30, Haddonfield, 50 and 
Greenwich 5 miles from the ocean, or from wide ocean tributaries, while 
Kelley's Island, as the name indicates, is surrounded by water. The 
daily range of temperature is higher the farther the station is removed 
from the influence of water and also the more remote the station the 
lower is its mean atmospheric humidity and the lower its mean dewpoint. 
In other words, those stations close to large bodies of water enjoy a 
climate more equable in temperature and consequently less subject to 
frost injury. 

The interchange of heat and equalization of temperature in the 
vicinity of bodies of water is favored by a gentle breeze but it will occur 
to a certain extent when there is practically no air stirring at inland 
points. The water is itself responsible for a certain amount of air move- 
ment and the attendant air drainage. It is almost needless to state that 
the larger the body of water the greater is its influence on air movement 
and air temperature. Much, too, depends on the topography in the 



ORCHARD LOCATIONS AND SITES 649 

immediate vicinity of the body of water. For instance, the so-called 
"fruit belt" on the eastern shore of Lake Michigan varies in width from 
less than 2 to over 20 miles. The lake is as wide where the belt is narrow 
as where the belt is wide, but the lay of the land is quite different. As a 
rule but little influence of the water is felt back of the crest of the slope 
toward the lake, bay or river and frequently its influence does not extend 
to the crest of the slope. Naturally, if the slope is gradual the influence 
is likely to be felt further back than if it is abrupt. 

Influence of Size and Shape of Body of Water. — Something of the 
relation between the size of the body of water and that of the area 
influenced by it may be understood by comparing the width of the fruit 
belts bordering Lake Michigan or Lake Ontario with those bordering 
Lakes Seneca or Canandaigua in New York. As already stated, the 
Michigan fruit belt is from 2 to 20 miles wide. The fruit belt along 
Lake Ontario is of equal width. Lakes Seneca and Canandaigua, them- 
selves only about 4 miles wide at the most, have distinct fruit belts only a 
quarter of a mile to 2 miles in width. A deep body of water has a much 
greater influence on the climate of the adjoining land than one which is 
shallow. The water is in effect a heat sponge, absorbing heat whenever 
air temperatures rise above the mean and liberating heat whenever they 
fall below it. Naturally, then, the larger this sponge the greater is its 
absorbing and liberating capacity. This is particularly important in 
the case of bodies of water so deep that they seldom freeze over or 
remain frozen for only a short time, as it relates to their modifying 
influence on midwinter minimum temperatures. On the other hand 
many lakes as wide as the finger lakes of central New York, because they 
are very shallow, furnish little protection to the neighboring slopes. 
Protection is likely in the vicinity of large rivers, especially if they are 
deep. Their currents, which delay or prevent their freezing over, may 
partly compensate for their lack of depth; a river 10 to 20 feet deep and a 
quarter of a mile wide may afford as much protection to orchards along 
its course as a lake twice that depth and of the same width. Indeed it is 
likely to afford greater protection because of its channel down which the 
cold air may continue to drain indefinitely. 

Indirect Temperature Effects. — Bodies of water influence temperatures 
in their vicinities in other ways than through promoting air drainage. 
There are certain favored spots where the increased atmospheric humidity 
due to proximity of water leads to the frequent formation of fog during 
periods when dangerously low temperatures occur at nearby points and 
a very effective check is thus placed on loss of heat by radiation. 
Kelley's Island in Lake Erie has been noted as a place thus rendered 
especially suited to the culture of comparatively tender long-season 
fruits and without doubt this is one of the chief factors in making possible 
the successful culture of European plums in the vicinity of Ste. Anne de 



650 



FUNDAMENTALS OF FRUIT PRODUCTION 



Beaupre" in Quebec, 200 miles north of the general northern limit for the 
same varieties. 

Probably it would be difficult to separate entirely the different 
influences of bodies of water upon climate, assigning to air drainage or to 
increased atmospheric humidity exact figures representing their pro- 
tective effects. The fact, however, that these other protective influences 
are at work does not lessen in importance the air drainage that is asso- 
ciated with water surfaces. 

Minor Temperature Effects. — Even small bodies of water have meas- 
urable, though slight, influences on temperature. Observations of mini- 
mum temperatures near a stream 40 feet wide in England, summarized 
in Table 13, show that the extent of the influence varies. 

Table 13. — Average Minimum Temperatures (Centigrade) At and Near River 

Bank 60 
(Six inches above ground) 





Station 6, 196 

feet from river, 

degrees 


Station 8, on river 
bank (straight 
part), degrees 


Station 7, on river 

bank (confluence 

of river and 

ditch), degrees 


Minimum all nights 


2.2 


3.0 


3.3 


Excess on river banks 




0.8 


1.1 


Minimum still nights 


0.0 


0.9 


1.4 


Excess on river banks 




0.9 


1.4 


Minimum nights with south 








or southeast wind 


3.5 


4.4 


5.4 


Excess on river banks 




0.9 


1.9 


Minimum nights with north 








or northeast wind 


1.6 


2.0 


2.5 


Excess on river bank 




0.4 


0.9 



Importance during the Winter. — Attention has been called particularly 
to the effects of air drainage on temperature during the soring and fall 
months and its bearing on the occurrence of frosts. It should not be in- 
ferred, however, that air drainage does not take place during other sea- 
sons where elevation and topography make it possible. Figures 69 and 
70 show differences in minimum temperatures during some of the winter 
months between stations at unequal elevations in a mountain valley in 
Utah. These range between 2° and 8°F. on the coldest nights for stations 
having 64 feet disparity in elevation and are about 10° for stations having 
350 feet variance in altitude. Such differences in minimum temper- 
atures during midwinter may often influence the amount of certain kinds 
of winter injury or winter killing experienced. Air drainage, therefore, is 
sometimes of as great importance in preventing winter injury as it is in 



ORCHARD LOCATIONS AND SITES 



651 



warding off injury from late spring or early fall frosts. Indeed, there are 
certain sections in which and certain fruits with which elevation to secure 
air drainage is of greater importance in dealing with midwinter freezing 
than with spring frost. The bark and trunk splitting occasionally 



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Fig. 69. — The minimum daily temperature for a bench land and a valley bottom 
station during 9 clear, autumn nights. {After Batchelor and West 2 ) 



accompanying sudden midwinter drops in temperature in the compara- 
tively mild climate of the Willamette valley is a case in point. 

Obstructions. — Air drainage is often impeded more or less seriously 
by obstructions of one kind or another, such as a stone wall, a hedge or a 
high board fence, a mass or belt of shrubbery. Thus it happens that a 



652 



FUNDAMENTALS OF FRUIT PRODUCTION 



natural or artificial planting sometimes serving admirably as a wind break 
and protecting the orchard at certain seasons, hinders air movement on 
calm nights to such an extent that little of the frost protection naturally 
expected from the orchard's elevation is actually obtained. No rules can 
be given for dealing effectively with these hindrances to air drainage, but 
the whole question should be considered on the ground when selecting an 
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December, 1913 January, 1914 

Fig. 70. — Minimum temperatures for stations of different elevations during 12 clear, 
calm, winter nights. (After Batchelor and West 2 ) 



LOCAL VARIATIONS AND THEIR SIGNIFICANCE 

Data have been presented showing that points only a few miles apart 
sometimes, because of topographic peculiarities, present climatic 
differences great enough to be of considerable importance in fruit growing. 



ORCHARD LOCATIONS AND SITES 



653 



The magnitude of such disparities often found between points on the 
same farm and occupying positions differing little in elevation or exposure, 
is not appreciated. Their influence is often subtle, but nevertheless real. 
They may make the difference between the necessity of one or of three 
applications of a fungicide, an interval of a week in the time of partic- 
ular spray applications, or of a week in the blossoming or maturing seasons 
of a fruit. 

Temperature. — It is not the intention in this discussion to present 
further data on the influence of a certain number of "heat-units'.' in 
bringing to particular stages of maturity plants of different kinds. 
However, mention may be made of the variation in the mean temperature 
between stations only a short distance apart. MacDougal 42 presents 
data showing that, of two stations in the New York Botanic Garden only 
a few hundred yards apart and presenting no great difference in elevation, 
one received 78,836 hour-degrees of heat in 1 year and the other only 
68,596. One of these points registered a temperature below freezing 
during 1478 hours in the course of the year and the other during 1736 
hours. Here is a difference of 13 per cent in heat units; in other words, 
one station enjoyed a temperature that was equivalent to an active grow- 
ing season of about 11 days longer than the other. Such a disparity is 
large enough to account for the difference between success and failure 
with many fruit crops, as for instance grapes, along the northern limits 
of their cultural range and it shows the importance to the grower of study- 
ing carefully the local variations often found within the limits of a single 
farm. 

Equally or even more striking are the figures recording the temper- 
atures of two stations on the campus of the University of California at 



Table 14. — Showing Variations in Temperature Between Two Stations on 
the Campus of the University of California 6 



Month 



Mean 
monthly maximum 



Mean 
monthly minimum 



Maximum 



Minimum 



September, 1902 

April, 1903 

May, 1903 

June, 1903 

July, 1903 

August, 1903 
September 1903 

April, 1904 

May, 1904 . . 

June, 1904 

Average 



79.3 
62.3 
70.8 
74.5 
75.6 
77.4 
76.6 
66.7 
76.2 
80.5 



73.4 



71.4 
62.0 
66.9 
73.4 
70.0 
69.6 
70.2 
64.5 
70.0 
71.7 



69.0 



54.5 
36.8 
43. 1 
49.7 
50.0 
48.2 
48.3 
42.5 
45.8 
47.9 



55.8 
44.7 
48.3 
52.3 
52.0 
51.9 
52.2 
46.5 
49.4 
51.3 



46.7 



50.4 



94 

74 

84 

108 

100 

86 

102 

88 

92 

98 



83.2 
70.0 
79.1 
101.1 
94.0 
78.9 
91.7 
82.9 
85.3 
92.8 



48 
32 
34 
36 
44 
44 
44 
34 
38 
42 



92.6 



85.9 



39.6 



49.0 
36.6 
42.6 
42.4 
46.8 
49.0 
46.0 
37.2 
40.6 
48.2 



43.8 



654 FUNDAMENTALS OF FRUIT PRODUCTION 

Berkeley, presented in Table 14. Though these stations were 120 feet 
apart in elevation, elevation alone cannot be held responsible for the 
differences recorded, for, as mentioned elsewhere, the influence of ele- 
vation on mean temperature amounts to only 4°F. for each 1000 feet. 
Without doubt many factors contribute to these local variations in tem- 
perature, some being more important in one case and others in another. 
It is not so important that all these factors be known and exactly evaluated 
in every instance as it is that their combined effect be recognized and 
properly utilized. 

Evaporation, Rainfall and Other Factors. — It is generally recognized 
that some spots or some locations are more subject than others to the 
drying action of the wind; however, the extent and importance of differ- 
ences in this respect are not generally recognized. Gager 12 records results 
of evaporimeter experiments in the New York Botanic Garden in 1907 that 
are particularly interesting. Three specially constructed evaporimeters 
were placed at several points in the garden; one was on a dry rocky knoll 
partly shaded by trees; a second was on low, poorly drained, marshy 
ground, also partly shaded and the third was in the open on well drained 
ground with sod on the one side and cultivated ground on the other. The 
evaporation losses from these different instruments between June 3 and 
October 14 were equivalent to 8.47, 4.84 and 12.10 inches, respectively. 
The precipitation during the same period was 9.32 inches. At the first 
station precipitation exceeded evaporation loss by only 0.85 inch, at the 
second station by 4.48 inches, while at the third station the evaporation 
loss exceeded precipitation by 2.78 inches. In commenting on these 
data, Gager says: "It should be kept in mind that the loss of water 
from the evaporimeters is not a measure of the amount of water lost by 
the soil through evaporation, but it is only an index of the evapor- 
ating power of the air for the given station. For the same locality the 
rate of evaporation from soil and from evaporimeter will materially 
differ, being less from soil and varying with its nature and condition, as 
well as with the surroundings above the soil surface." Nevertheless at 
one station the evaporation losses were between two and three times those 
at one of the others and such a difference may often be enough to have a 
great influence on plant growth and crop yield. 

Local variations in rainfall are likely to be especially large in sections 
showing considerable difference in elevation, but they are often important 
where the elevations are substantially the same. Thus at Davis, Cali- 
fornia, when the annual rainfall was 16 inches, it was about 25 inches at 
a point ten miles to the west and having the same elevation. Thirty 
miles still further west, but in the foothills of the Coast Range, it was 
over 50 inches. 

With the local variations in temperature and humidity there are often 
important differences in the prevalence of insects and diseases that, 



ORCHARD LOCATIONS AND SITES 655 

independent of direct influence of the environment on the plant, may 
set definite limits to the profitable culture of certain fruit varieties. 

There may be also minor local variations in their life histories which 
modify the effectiveness of spraying treatments. The best time for a 
certain spray in one neighborhood may differ several days from that for 
another neighborhood not far away. 

Summary. — The selection of a location for fruit production, or of 
kinds and varieties of fruit to be grown in a particular location, involves 
a consideration and application of the same general principles. The 
more important economic considerations are the cost of land and the 
nearness and character of transportation facilities. The overhead charge 
due to cost of land should never exceed 10 per cent, of the value of the 
product at the orchard and should not amount to more than half that 
figure. The cost of hauling to the local market or to a shipping station 
should levy no greater tax against the total income. Other factors, 
such as fruit product establishments and cooperative shipping organiza- 
tions affecting the ability to dispose of products quickly and advantage- 
ously are important in commercial production. 

Different slopes offer quite distinct environmental conditions for 
the growth of the plant and certain slopes may be much preferred to 
others for certain fruits when grown in some sections, though the reverse 
condition may hold for the same varieties in another section. These 
environmental differences can be profitably capitalized in many cases 
if kinds and varieties are selected so as to obtain the closest adaptation 
to the particular farm or parts of the farm. The same may be said of 
minor inequalities in temperature, rainfall and evaporation between 
near by points that possess nearly the same elevation and exposure. 

Factors of great importance in determining danger from late spring 
and early fall frosts are the air drainage incident to unequal eleva- 
tion and the proximity to bodies of water. Often comparatively small 
disparities in elevation (25 to 50 feet) make a considerable difference in 
danger from frost injury. This influence is important also in determining 
the amount of damage from midwinter freezing. Proximity to large 
bodies of water, particularly on their windward side, affords considerable 
protection from extremes of climate. The range of influence of such 
bodies of water varies with their size and depth and with the topography 
of the adjoining slopes. 



CHAPTER XXXV 
ORCHARD SOILS 

All field crops are influenced more or less by the kind of soil in which 
they are grown. The same may be said of all fruit crops. Just as some 
land is classed as good for general crops so some may be classed as good 
for orchard fruits and just as some is considered good for wheat but poor 
for alfalfa, so some may be good for pears but poor for strawberries. In 
a way the factors that are important in determining the value of a particu- 
lar soil for field crops are also important in determining its value for fruit 
production. However, were the judging of soils for general farming 
purposes and for orcharding to be placed on a score-card basis the cards 
would differ considerably in a number of respects. 

For field crops, both surface soil and subsoil are important in deter- 
mining relative value of the land but the surface soil is generally regarded 
as of far greater importance. For fruit crops in general they are of more 
nearly equal significance. Indeed there are many conditions presented 
in which there is little doubt but that the nature of the subsoil is more 
significant than that of the surface soil. For field crops physical and 
chemical conditions are generally considered of substantially equal 
importance in determining productivity and suitability to individual 
crops. Though chemical composition is likewise important in the produc- 
tion of trees and other fruit plants, physical condition is a first considera- 
tion. The fact that certain fruits, such as the apple, are grown with equal 
success in some of the heavy clay loams of western New York, the light 
sandy loams of New Jersey, the loess bordering the Missouri River, the 
adobes of the Rogue River valley, Oregon and the volcanic ash of the 
Hood River section of Oregon appears to contradict this; nevertheless 
closer analysis reveals certain common characteristics of their physical 
condition — a similarity much greater than is shown in a comparison of their 
chemical composition. 

CONSIDERED FROM THE STANDPOINT OF PHYSICAL CONDITION 

Chief among the physical characteristics desirable in an orchard 
soil are porosity and thorough aeration, coupled, if possible, with depth. 
The loess soils of the Mississippi, Missouri, Rhine and Hoang-ho val- 
leys are among the best in the world for the fruits that will grow in 
the climates of these respective regions because they are extremely deep, 

656 



ORCHARD SOILS 657 

drainage is practically perfect (the water table often being 50 or more 
feet below the surface) and they are so well aerated that tree roots often 
penetrate to a depth of 20 feet and ordinarily to depths of 6, 8 or 10. 
In the Rhine valley grape roots have been traced to a depth of 15 meters. 
Similar conditions exist in some of the volcanic ash soils of the Pacific 
Northwest and the alluvial soils and bench lands of many river valleys 
in Washington, Idaho, Oregon and California. One of the main reasons 
certain of the arid soils of California have proved so well suited to fruit 
growing is that the surface soil grades insensibly into the subsoil and 
that the latter is well drained and thoroughly aerated; hence roots 
penetrate to great depths and sustain the plant when the surface soil 
may become too dry. 27 That good drainage and its corollary good 
aeration are associated with this condition is indicated by Hilgard 28 
when he states that with the rise of the water table in such soils through 
injudicious irrigation trees that had thrived may actually suffer, much 
as those planted in shallow soil or soil underlaid with an impervious 
hardpan and from practically the same causes. 

The extent to which the success of the fruit plantation depends on 
these two factors, drainage and aeration, is not generally realized. In 
speaking of the soil requirements of the papaya Higgins 24 says: "There 
are few, if any, soils in which the papaya will not grow if aeration and 
drainage are adequately supplied. Most of the plantings of this Station 
are upon soils regarded as unsuitable for other fruit trees, and upon 
which the avocado is a failure. . . . They are very porous, permitting 
a perfect drainage and aeration." The same writer goes so far as to 
say, "There are two essential features of a good banana soil. The 
first is abundant moisture, the second, good drainage." 23 In speaking 
of the soil requirements of forest trees one authority maintains that 
almost any soil is capable of producing any kind of timber if the moisture 
requirements are satisfied. 22 Even the blueberry, which is often classed 
as a semiaquatic or bog plant, requires a well aerated medium for its 
roots and does not, contrary to appearances, send them down into the 
water or into waterlogged soil. 7 Obviously, certain shallow rooted 
species such as the strawberry do not require and could not make full 
use of a soil of the depth best suited to one of the tree fruits, but even 
the strawberry will do much better in a soil that is moderately deep 
(say, two and one half to three feet) and well drained than in one that is 
shallow or poorly drained and poorly aerated. 

Requirements of Different Crops. — However, there are marked 
differences between species and even between varieties of the same 
species in their preferences for soils of unlike textures. The peach 
and almond flourish only in soils of a comparatively light porous texture, 
while the pear and quince prefer at least moderately heavy soils and will 
often do well in extremely heavy soils. The pomegranate is reported as 

42 



658 FUNDAMENTALS OF FRUIT PRODUCTION 

doing fairly well in soils ranging from almost pure sand to heavy clay, 
but it does its best only in those that are fairly heavy and well drained ; 
however, it will endure a wet, poorly aerated soil much better than 
most fruit plants. 29 Probably nowhere in the world does the pineapple 
do better than along the east coast of Florida, between Fort Pierce and 
Lake Worth, where the soil is almost a pure white sand (containing 
actually upwards of 98 per cent sand, gravel and silt); 63 nevertheless 
they are grown very successfully on some of the heavy soils of the Hawa- 
iian Islands. It is generally recognized, however, that the soil that 
may be best for a particular fruit or some particular variety in one sec- 
tion may not be best in another section with different climate and distinct 
environmental conditions. Thus in New York the Concord grape 
grows on a wide variety of soils but seems to prefer a fairly strong loam 
with considerable clay; in western Washington the same variety can 
be grown successfully only in light sandy or sandy loam soils that tend 
to hasten maturity of fruit and vine. In general, the more favorable 
the texture of the soil for both the lateral and vertical development of 
the root system, the better. 

Requirements as to Depth. — Theoretically, a soil need be only half 
as rich as another in order to support equally well a certain amount 
of vegetative growth if it is of such a character that roots penetrate 
twice as deep. Furthermore, since water is a limiting factor as often 
as plant nutrients, a tree with the deeper root system, though in poorer 
soil, is really in a better position than one growing in a richer, but shal- 
lower, medium. Only under very special conditions should ordinary 
deciduous tree fruits be planted in a soil in which the roots cannot pene- 
trate freely to a depth of 2% to 3 feet in humid regions and to a depth of 5 
to 10 feet in arid and semi-arid regions; soils that will permit greater pene- 
tration are preferable. Shallowness of soil, hardpan or plowsole close to 
the surface, impervious subsoil and poor drainage are interrelated factors 
which check vegetative growth, reduce yields and the size, quality and 
grade of the fruit, favor irregular bearing and lead to numerous physio- 
logical troubles, the treatment of which is difficult. 

Classification of Soils According to Size of Soil Particles. — Since 
there is occasion repeatedly to refer to soils of different physical structure, 
a classification based on mechanical analysis, as used by the Bureau 
of Soils of the Federal Department of Agriculture, is presented here 44 
(see Table 15). 

It should be noted in connection with this classification that no 
account is taken of gravel or stones above 2 millimeters in diameter. 
Many soils contain rock particles larger than this maximum and not 
infrequently these constitute a large proportion of the soil volume. 
Accordingly a soil that in this scheme would be classified as a silt or even 
a clay might in fact be gravelly or rocky or stony in character. Though 



ORCHARD SOILS 



659 



these larger components may have a relatively unimportant bearing on 
water holding capacity, aeration, root penetration and related features, 
they do influence it materially in its relation to tillage practices and they 
often prove a limiting factor in determining the kind of crop that can 
be grown in it advantageously, or the kind of orchard culture that must 
be practiced. Thus of two soils whose so-called "fine earth" might ana- 
lyze the same, one might be suitable to the strawberry and the other 
quite unsuited because of the presence or absence of large quantities 
of rocks and coarse gravel. It is interesting to compare the mechanical 
analyses of several soils used for fruit production. 



Table 15. — Scheme of Soil Classification, Based on the Mechanical 
Composition of Soils 



(1), (2) 
2-0.5 
milli- 
meters, 
per cent. 



(1), (2), (3) 
2-0.25 
milli- 
meters, 
per cent. 



(6) 
0.05-0.005 
milli- 
meters, 
per cent. 



(7) 
Less than 
0.005 
milli- 
meters, 
per cent. 



(6), (7) 
Less than 
0.05 
milli- 
meters, 
per cent. 



Coarse sand 

Medium sand . . . 

Fine sand 

Sandy loam 

Fine sandy loam 

Loam 

Silt loam 

Clay loam 

Sandy clay 

Silty clay 

Clay 



>25 
<25 



>50 
>20 
<20 
>20 
<20 



0-15 

0-15 

0-15 

10-35 

10-35 

<55 

>55 

25-55 

<25 

>55 



0-10 
0-10 
0-10 
5-15 
5-15 

15-25 
<25 

25-35 
>20 

25-35 
>35 



<20 

<20 

<20 

>20<50 

>20<50 

>50 

>60 
<60 

>60 



(1) "Fine gravel," 2-1 millimeters. (2) "Coarse sand," 1-0.5 millimeters. (3) 
"Medium sand," 0.5-0.25 millimeter. (6) "Silt," 0.05-0.005 millimeter. (7) 
"Clay," less than 0.005 millimeter. The residue is composed of "fine sand," 0.25-0.1 
millimeter and "very fine sand," 0.1-0.05 millimeter. 

Mechanical Analyses of Various Fruit Soils. — Soils A and C with their 
subsoils B and D (Table 16) are fairly typical of the western New York 
fruit district, one of the leading apple producing sections of the world. 
Soil A, the Dunkirk sandy loam, contains 64 per cent, of medium and 
coarse sand in the surface and slightly more in the subsoil and only 
about 5 per cent, of clay in both surface and subsoil, while soil C, the 
Dunkirk loam, contains only about 30 per cent, of medium and coarse 
sand in the surface soil and a little more than half that amount in the 
subsoil, but approximately twice as much of the finer materials — clay 



660 FUNDAMENTALS OF FRUIT PRODUCTION 

and silt. Here, indeed, are marked differences in the average size of 
soil particles, yet there are but slight differences in the way apple trees 
grow in these soils. Soil E, a fairly typical loess of Nebraska, contains 
no medium or coarse sand and comparatively large amounts of silt and 
clay, yet it furnishes excellent drainage and is eminently suited to the 
production of fruit, particularly apples. Though probably the Billings 
clay loam (Soil M), with its 47 per cent, clay and 91 per cent, of clay and 
silt combined is not an ideal soil for apples, it is a characteristic soil of the 
Grand Junction section of Colorado and where the topography permits 
reasonably good drainage, apple production is profitable. This par- 
ticular soil serves to illustrate the point that the mechanical analysis of a 
soil is not always an accurate index to its possibilities for fruit growing. 
Though this analysis suggests very poor drainage and consequently a 
lack of suitability for fruit crops, some of this land is fairly well drained 
and does produce good fruit crops. However, it is but proper to state 
that the majority of the Grand Junction orchards are on soils of a some- 
what lighter character. The Maricopa gravelly sand of California is, 
as the name suggests, comparatively light and open in character, con- 
taining 57 per cent, fine, medium and coarse sand and 11 per cent, fine 
gravel. It is considered very good for grapes; yet the Alamo clay adobe 
with 95 per cent, of clay and fine silt is said to be fairly suitable for grapes 
where the topography is such that drainage is not particularly poor. 59 
Probably the gray-brown clay of Sonoma, California, whose mechanical 
analysis is shown in column in the table, represents more nearly average 
soil conditions for the grape. Certainly it produces some of the best wine 
grapes of the country. 42 Citrus fruits likewise thrive on soils ranging 
from heavy adobes to gravelly loams and gravelly sands. It is interesting 
to note the texture of one of the pineapple soils of the Florida coast 
(Soil H in the table) — over 98 per cent, fine, medium and coarse sand. 
The mechanical analyses of many other fruit soils which might be 
included would furnish little information, beyond that already given, 
as to the actual soil requirements of the different fruits. It is evident 
that* the mechanical analysis of a soil carries some suggestion as to its 
suitability for fruit crops of different kinds but it is an index only in so far 
as it is an index of texture, drainage and aeration; these qualities depend 
to a considerable extent on such factors as topography, hardpan, chemi- 
cal composition, rainfall and the movement of underground water. 
In other words, it is hardly practicable to attempt exact definition, in 
terms of soil particle measurements, of the soil requirements for distinct 
varieties of the same fruit or even of different fruits. 

CONSIDERED FROM THE STANDPOINT OF CHEMICAL COMPOSITION 

The statement has been made that, broadly speaking, the physical 
condition of the soil is more important in fruit production than is its 



ORCHARD SOILS 



661 



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662 FUNDAMENTALS OF FRUIT PRODUCTION 

chemical composition. However, it should not be inferred that chemical 
composition is of little significance, or that poor soils are preferable to 
good soils for orchard purposes. On the contrary, the richer the soil 
the better, though productivity as it concerns the orchardist, may be quite 
different from productivity as it concerns the man growing cereals or fiber 
plants and a soil that is productive in pineapple cultivation may be 
unproductive in avocado or prune cultivation. The only satisfactory 
measure of soil productivity is in terms of crop production of the specific 
plant under consideration. Hardly an orchard of commercial size any- 
where fails to show differences in individual tree growth and production 
due apparently to variation in soil. However, thorough examination 
would show that many such differences are related to variations in texture 
or in water-holding capacity rather than in chemical composition. Often 
the great inequalities between the size, longevity or productivity of trees 
in various fruit producing sections may be regarded as due largely to 
chemical composition. The average differences between the apple 
orchards of western New York and southern Ohio is a case in point — a 
fact emphasized by the response of the orchards of the latter section to 
proper fertilizer applications. 

Requirements of Different Crops. — It should be recognized, too, that 
certain fruits are particularly favored by the presence of some element or 
compound in the soil. For instance, a high lime content is said to be 
particularly favorable for oil production in the olive. 34 The cherry like- 
wise seems to respond favorably to lime. Vitis berlandieri flourishes in, 
even prefers, a limestone soil; but V. labrusca is intolerant of lime. 19 The 
chestnut has been shown to be subject to chlorosis on soils containing 
upwards of 3 per cent, lime 9 and pears are reported as frequently 
chlorotic on calcareous soils. 49 Many crop plants are known to prefer 
a nearly neutral soil reaction and it has consequently been assumed that 
most fruit plants do; some, however, as the strawberry, thrive only in an 
acid medium and the blueberry demands a markedly acid soil. 7 Certain 
fruits like the grape are very tolerant toward "alkali;" others, like the 
mulberry, are very sensitive to it. The pineapple is intolerant of man- 
ganese. 33 These and the many other peculiarities of a fruit must be 
kept in mind and soils selected accordingly or, conversely, the soil's 
peculiarities must be ascertained and the fruit species or varieties selected 
accordingly. 

Much can be done toward adapting a number of fruits to an uncon- 
genial soil by growing them on a stock suited to the soil in question. 
This matter is discussed in some detail in the section on Propagation. 

Chemical Analyses of Various Fruit Soils. — In the accompanying 
tables (17 to 22) are presented chemical analyses of certain typical soils 
that are more or less noted for fruit production, together with the analyses 
of certain other soils that have unknown value for fruit production or that 



ORCHARD SOILS 



663 



are definitely known to be unsuitable. Comparison may thus be made 
between "fruit" soils and soils in general and between good and poor 
fruit land. 

Table 17. — Chemical Analyses of Average Soils of Humid and Arid Regions 
and of Certain Orchard Soils in Asia Minor and California 





A, average of 
analyses of 313 

soils of arid 

regions, 26 per 

cent 


B, average of 
analyses of 466 
soils of humid 
regions, 29 per 
cent 


C, soil from 
Erbelli, Asia 
Minor (noted 
for fig produc- 
tion), »» per cent 


D, Mesa loam 
from near 

Riverside, Cali- 
fornia, 25 per 
cent 




70.565 
7.266 
0.729 
0.264 
1.362 
1.411 
0.059 
5.752 
7.888 
0.117 
0.041 
1.316 
4.945 


84.031 
4.213 
0.216 
0.091 
0.108 
0.225 
0.133 
3.131 
4.296 
0.113 
0.052 

3.644 


1.00 
99.00 

76.33 
5.35 
1.09 
0.19 
1.96 
1.56 
0.01 
6.49 
3.25 
0.29 
0.06 
1.00 
2.29 


25.00 




75.00 


Analysis of fine earth: 

Insoluble matter 


63.67 
13.70 


Potash (K2O) 


0.73 


Soda (,Na20) 


0.36 


Lime (CaO) 


1.58 




1.85 


Manganese oxid (MnsOO 

Ferric oxid (Fe203> 


0.03 

10.02 

5.06 


Phosphorus pentoxid I P2O6) 

Sulfur trioxid (SO3) 


0.07 
0.01 






Water and organic matter 


2.74 


Totals 


99.993 
0.750 

15.870 
0.101 


100. 178 
2.700 
5.450 
0.122 


99.87 
0.27 


99.82 




0.20 











Table 18. — Chemical Analyses of Typical Fruit Soils of Washington 53 



A, upper 
bench land, 
Wenatchee, 

per cent 



Insoluble silica 

Hydra ted silica 

Soluble silica (Si02) 

Potash (K2O) 

Soda (Na 2 0) 

Lime (CaO) 

Magnesia (MgO) 

Manganese dioxid (M113O4). 

Iron oxid (Fe203) 

Alumina (AI2O3) 

Phosphorus pentoxide (P2O 

Sulfur trioxid (SO3) 

Carbon dioxid (CO2) 

Volatile and organic matter 

Total 

Humus 

Total nitrogen (N) 



81.632 
2.498 
0.316 
0.518 
0.233 
0.714 
0.186 



4.760 
6.145 
0.225 



2.969 



100. 176 
1.942 
0.061 



B, volcanic [ C, Kenne- 

ash, Walla | wick sand, 

Walla, per Kennewick, 

cent I per cent 



77.772 
5.464 
0.543 
0.328 
0.238 
0.659 
0.104 



4.601 
3.925 
0.037 



5.580 



99.251 
1.400 
0.055 



84.402 
3.332 
0.265 
0.312 
0.416 
0.944 
0.650 
trace 
4.505 
5.889 
0. 140 
0.018 



1.219 



D, sandy 

soil, Vashon 

Island, per 

cent 



100.040 
0.465 
0.035 



76. 652 
8.572 
0.348 
0.126 
0.106 
0.615 
0.807 



3.064 
4.852 
0.044 



4.467 



99.653 
1.870 
0.077 



E, sandy 

soil, Vashon 

Island, per 

cent 



72.297 
8.646 
0.062 
0.157 
0.167 
0.693 
0.548 



3.023 
7.634 
0.073 



6.075 



100. 275 
3.100 
0.174 



664 FUNDAMENTALS OF FRUIT PRODUCTION 

Table 19. — Chemical Analyses of Certain Oregon Soils 50 





"Redhill" 

land, Salem, 

per cent 


White land, 

Benton 

County, 

per cent 


Adobe soil, 

Benton 

County, 

per cent 


Sandy loam, 

Wasco 

County, 

per cent 


"Shot" land, 

Multnomah 

County, 

per cent 


Character of soil: 
Analysis of fine earths: 


28.88 
71.12 

68.48 
4.38 
0.47 
0.33 
0.40 
0.96 

14.78 

0.63 
10.19 


16.50 
83.50 

70.26 
5.53 
0.06 
0.07 
0.66 

0.04 
13.51 

0.05 

0.03 

10.13 


2.25 
97.75 

38.91 
16.74 
0. 11 
0.03 
1.60 
1.78 
0.08 
23.21 

0.01 
17.44 


25.50 
74.50 

63.65 
12.65 
0.12 
0.16 
1.41 
1.10 

9.23 

0.28 
11.81 


34.00 
66.00 

67.40 


Soluble silica (SiCM 

Potash (K2O) 

Soda (Na 2 0) , 

Lime (CaO) 


5.18 
0.28 
0.05 
1.35 
0.90 




0.40 
17.67 






Sulfuric acid (SO3) 

Phosphoric acid (P2O5) 

Water and organic matter . . 


0.82 
0.34 

7.98 


Total 


99.72 
0.52 


100.34 
1.22 


100.00 
1.80 


100.41 
4.42 


100.07 
1.76 







Table 20. — Chemical Analyses of Certain Florida Soils 



A, surface soil, 
West Palm 

Beach«« (pine- 
apple land), 
per cent 



B, subsoil, 
West Palm 
Beach 46 (pine- 
apple land), 
per cent 



C, surface soil 
Volusia 

County 48 
(orange land), 

per cent 



D, surface soil, 

muck land 48 

(fruit and 

truck), 

per cent 



Silica (Si02) insoluble 

Silica (SiO-2) soluble 

Lime (CaO) 

Magnesia (MgO) 

Potash (K2O) 

Iron and alumina (Fe203 and AI2O3) 

Phosphorus pentoxid (P2CH) 

Sulfur trioxid (SO3) 

Volatile matter 

Humus 

Nitrogen (N) 

Chlorin 

Water and organic matter 



99.3070 
0.0147 
0.0037 
0.0000 
0.0048 
0.2210 
0.0100 
0.0038 
0.4860 
0. 2000 
0.0100 



99.5840 
0.0197 
0. 0000 
0.0000 
0.0126 
0. 2400 
0.0087 
0.0038 
0. 1620 
0.0675 
0. 0045 



96. 0852 



0.0526 
0.0145 
0.0208 
1.1726 
0. 1600 
0.0096 



0. 0890 

trace 

2.3910 



53. 5900 



trace 
trace 
0. 1500 
10.0100 
trace 
0.0500 



1.500 

0.0200 

34.9700 



ORCHARD SOILS 665 

Table 21. — Chemical Analyses of Manganiferous and Normal Soils of Oahu 36 



Constituents 



Manganiferous soil 



Soil 



Subsoil 



Normal soil 



Soil 



Subsoil 



Insoluble matter 

Potash (K 2 0) 

Soda (Na 2 0) 

Lime (CaO) 

Magnesia (MgO) 

Manganese oxid (Mn 3 4 ) . . 

Ferric oxid (Fe20a) 

Alumina (A1 2 3 ) 

Phosphorus pentoxid (P2O5 

Sulfur trioxid (S0 3 ) 

Titanic oxid (TiOj) 

Loss on ignition 

Total 

Nitrogen (N) 



33.46 
0.83 
0.40 
1.39 
0.55 
9.74 

19.65 

15.50 
0.21 
0.16 
0.73 

19.93 

100.35 
0.39 



36.06 
0.74 
0.42 
0.86 
0.43 
8.76 

21.51 

15.74 
0.16 
0.09 
1.09 

14.45 

100.31 
0.23 



40.89 
0.51 
0.21 
0.51 
0.37 
0.22 

35.72 
3.58 
0.07 
0.09 
3.83 

14.22 

100.22 
0.34 



39.25 
0.60 
0.32 
0.66 
0.38 
0.06 

33.28 
8.66 
0.08 
0.07 
2.74 

13.99 

100.09 
0.25 



Table 22. — Chemical Analyses of Miscellaneous Soils 



.4, Maricopa 

gravelly loam 

Arizona, 10 

per cent 



B, Peach belt 
soil. South 

Haven, 

Mich. ,35 per 

cent 



C, Olive or- 
chard soil, 

Ventura, 

Cal., 6 per 

cent 



D, Slate col- 
ored upland 
adobe Ala- 
meda, Cal., 4 
per cent 



E, Loess soil, 

Kansas City, 

Mo., 30 per 

cent 



Insoluble silica (Si02> 

Soluble silica (SiCh) 

Lime (CaO) 

Magnesia (MgO) 

Potash (K2O) 

Soda (NaaO) 

Ferric oxid (FesOa) 

Alumina (AI2O3) 

Phosphorus pentoxid (P2O5) 

Sulfur trioxid (SOj) 

Carbon dioxid (CO2) 

Chlorine 

Water and organic matter . . 

Humus 

Nitrogen (N) 



72.35 
10.29 
2.07 
1.36 
0.66 
0.28 
4.41 
4.94 
0.09 
0.03 
0.87 
0.03 

0.51 
0.04 



87.23 

0.51 
0.46 
0.83 
0.34 
1.52 
2.87 
0. 13 
0.20 



5.64 
0.07 



82.11 
6.88 
0.67 
0.57 
0.47 
0.42 
5.26 
1.30 
0.21 
0.09 



2.23 
0.78 

0.074 



64.790 
16. 564 
0.868 
0.978 
0.579 
0.100 
3.791 
7.718 
0.143 
0.006 



4.601 
0.697 



34.98 

1.70 
1.12 
1.84 
1.06 
2.36 
6.49 
0.09 
0.02 



666 FUNDAMENTALS OF FRUIT PRODUCTION 

Probably the most striking fact brought out in a study of the chemical 
analyses of fruit soils (Tables 17 to 22) is their extreme variability and 
their frequent wide divergence from the averages of the soils of either the 
humid or arid sections. It is impossible to associate certain extreme soil 
types with special crops. For instance a single fruit crop would hardly 
be expected to do equally well on soil like that shown in columns A 
and B of Table 20 and those shown in Table 21. The Oahu soils con- 
tain seven to 20 times as much phosphorus, 50 to 80 times as much potash 
and 30 to 40 times as much nitrogen as those of the Florida coast; the 
difference in some of the other constituents is as great or greater. Yet 
these soils are almost equally well suited to the pineapple, though their 
fertilizer requirements are somewhat different. The two Hawaiian soils 
shown in Table 21 resemble each other closely, much more closely than 
they resemble the Florida soil, but they show a marked disparity in their 
suitability for fruit culture and the soil that is the richer in the nutrient 
elements, nitrogen, potash and phosphoric acid, is the poorer when meas- 
ured in terms of pineapple production. Though the first three soils from 
Washington whose analyses are given in Table 18 show marked differ- 
ences in composition, especially in their phosphorus and nitrogen 
content, all are noted for their fruit production and proof that even a single 
fruit, as the apple, reaches a higher stage of perfection in one than in 
the others is difficult. The soil designated in Table 19 as "White land" 
does not differ greatly in its analysis from the "Redhill" or the "Shot" 
land, except that it contains less potash and phosphoric acid. These ele- 
ments are present, however, in larger amounts than in some of the other 
fruit soils whose analyses are given. Yet this "White Land" is not 
suited to fruit production and the "Redhill" land and the "Shot" land 
are among the best fruit soils of the state. The factor determining the 
difference betwen them is drainage. The analyses shown in columns D 
and E of Table 18 are particularly interesting in that both soils are from 
near by fields on Vashon Island, Washington. The differences in compo- 
sition as shown by the analyses are comparatively small; both are con- 
sidered well suited to strawberry culture and the average variety does 
well upon both soils. Yet the Clark variety is reported as thriving only 
on the one and as failing to produce satisfactorily on the other. 53 

Evidently the relation of the chemical composition of the soil to 
suitability for fruit growing is far from well understood, much less 
established. Without doubt different fruits and possibly distinct varie- 
ties of the same fruit require, or at least grow better in, soils of somewhat 
dissimilar chemical composition. However, since present methods of 
analysis do not differentiate clearly between those requirements they do 
not actually measure soil productivity as it is expressed in terms of fruit 
production and they do not afford a very accurate index to fruit crop 
adaptation. 






ORCHARD SOILS 



GG7 



Evidence on Soil Requirements from Fertilizer Experiments. — Point 
is lent the last statement by data presented in Table 23 assembled 
by Stewart, showing the response to fertilizer applications of trees growing 
in soils of varying productivity. In commenting on these data Stewart 52 
remarks: "These figures show that the correlation between soil composi- 
tion, as determined by the methods of soil sampling and analysis above 
specified, and the actual response of the associated trees to additional 
fertilization is either exceedingly slight or absent entirely. One would 
naturally expect that the largest response would appear where the chem- 
ical fertility of the soil was lowest, and vice versa. This evidently has not 
occurred. In fact, the least response to practically all types of fertiliza- 

Table 23. — Relation of Soil Composition to Fertilizer Response 

(After Stewart™) 



Soil type 



Nitro- 
gen 



.Phosphorus (P2O5) 



Per cent. Per cent, 
(total) (total) 



Per cent, 
(avail- 
able) 



Potash (K2O) 



Per cent 
(total) 



Per cent. 
( avail- 
able) 



Response to fertili- 
zation. (Per cent i 
crease in yield) 



K OF' 



Porters 

Montalto . . 
DeKalb... . 

Chester 

Volusia 

Lackawanna 

Frankstown 
Chenango. . . 
Hagerstown 



0.132 
0.071 
0.118 
0.158 
0.163 
0.300 

0.244 
0. 183 
0. 123 



0.093 
0.029 
0.087 
0.116 
0.132 
0.233 

0.161 
0.315 
0. 135 



0.017 
0.009 
0.002 
0.012 
0.007 
0.043 

0.032 
0.122 
0.006 



2.35 
0.66 

1.81 
2.23 

1.69 
1.78 

1.27 
1.55 
1.97 



0.020 
0.010 
0.029 
0.040 
0.045 
0.051 

0.026 
0.145 

0.042 



24 

3 
148 
15 
94 
27 
CF3 
16 
24 

9 



43 
29 

1S1 
24 
93 

144 

75 
26 
92 



20 

30 

294 

46 

117 

200 



1 Complete fertilizer. 2 Manure. 3 Per cent, increase in growth, instead of yield. 

tion has occurred in the soil analyzing poorest of all, and some of the largest 
responses have appeared in the chemically richest soils. The ordinary 
methods of soil analysis are not yet adequate to furnish a reliable indi- 
cation of the fertility needs of an orchard. Trees on chemically rich 
soils will not of necessity prove unresponsive to additional fertilization, 
nor will trees on chemically poor soils always prove responsive. In other 
words, some other indicator than the chemical composition of the soil, 
as here determined, must be relied upon to determine the real need of 
additional fertility in an orchard. At present, therefore, the surest and 
most delicate test yet devised for determining the fertility needs of an 
orchard soil is the actual response of the living tree in the soil concerned 
to appropriate fertility additions." 

The soil is a very complex substance and the soil solution likewise; 
apparently absolute amounts of certain elements or compounds that it 
contains are not so important as the state of balance or equilibrium 



668 FUNDAMENTALS OF FRUIT PRODUCTION 

existing between them. No better evidence to this effect is needed than 
some of the facts brought out by the analyses of the Florida and Hawaiian 
pineapple soils that have been mentioned. Certainly it would not be 
suspected from these analyses that in the Hawaiian soils with their 20 to 
35 per cent, of iron (indeed there is one local pineapple district in the 
Hawaiian Islands where the soil contains 85 per cent, iron and titanium 65 ) 
the plants often show symptoms of iron starvation and that iron sulphate 
is their most valuable fertilizer, though less than three-tenths of 1 percent, 
of iron furnishes an ample supply in the Florida sands. The relationship 
between soil and crop is more than that existing between the different 
factors in a problem in addition and subtraction. Other aspects of this 
general question are discussed in the sections on Water Relations and 
Nutrition. 

VEGETATION AS AN INDEX TO CROP ADAPTATION 

Though at present no single feature of the chemical or mechanical 
composition of the soil can be designated the chief cause for the way 
some fruit crops grow on it, soil differences, even slight differences, may 
be of great significance to the fruit grower. His study of soils should 
include more than the features brought into contrast by chemical and 
mechanical analyses. The types of the native vegetation may serve as 
very useful indices of probable productivity when planted to cultivated 
crop plants belonging to the same or a closely related genus or family; 
knowledge of plant ecology may make it possible to predict with accuracy 
the way some entirely unrelated plant will behave on the soil in question. 
For instance, in Ohio, land upon which the sugar maple, beech, oak, or 
chestnut thrive naturally is likely to be well suited to the apple, but land on 
which the elm is native is seldom desirable for that fruit. 17 In western 
Oregon and western Washington, hill land supporting a vigorous growth 
of the native "brake" or fern (Pteridium aquilinum pubescens) is charac- 
teristically good for prunes. In the Ozarks "post-oak" land is good for 
grape culture. Ney 47 has pointed out that the kinds of forest trees grow- 
ing on land often form something of an index of its chemical condition. 
He says, "As regards the chemical composition of the soil, even slightly 
sour marshy soils are unfavorable to all species of trees except alder, 
birch, and spruce; whilst sour soils, liable to dry up at certain seasons, 
are unsuited to all except birch, spruce, Scots and Weymouth pines." 
Ash, maple, sycamore, and elm require a moderate quantity of lime and 
beech, hornbeam, oak, as also larch and Austrian pine, thrive best on soils 
that have at least some lime in their composition. The hardwoods — oak, 
ash, maple, sycamore, elm, chestnut, beech and hornbeam — also appear 
to demand the presence of a considerable quantity of potash, while on the 
other hand, spruce, silver fir and especially Scotch pine and birch thrive 



ORCHARD SOILS 669 

on soils rich neither in lime nor potash. In Florida a dense growth of 
palmettos is likely to indicate an undesirable hardpan or subsoil; such 
soils should be avoided in citrus fruit plantings. 

Not only are the kinds of native trees or plants useful in determining 
the value of a soil for fruit growing, but the type of growth that these 
species make is of equal significance. Thus Vosbury 61 states, "Most of 
the recent citrus plantings in Florida have been made on high pinelands. 
Three grades of high pineland are recognized. The best grade is charac- 
terized by large straight-growing pines with occasional oaks, hickories, 
or other hardwood trees. The soil is a sandy loam, fairly rich in humus, 
and is underlaid with a clay subsoil at a depth of 6 feet or less. In 
second-grade pinelands the pine trees are smaller and there are few or no 
hardwoods, while the subsoil is further from the surface. In the third 
or poorer grade the pines are still smaller and scrubbier and the clay 
subsoil far below the surface soil." 

The soils picked as especially suited to certain field crops in some 
sections are less likely to furnish a reliable guide to their suitability to 
certain fruits. In New England apples will generally do well in those 
soils considered best suited to corn, for only the lighter earlier soils are 
able properly to mature that crop in that section, but in Illinois the best 
corn land is quite different in character and the best apple land is outside 
the corn belt. 



ADAPTATION OF VARIETIES TO PARTICULAR SOILS 

In addition to the more or less general soil requirements for different 
kinds of fruits that have been mentioned, particular varieties or groups 
exhibit certain soil preferences. 

For instance, in speaking of soil adaptations of plums, Hedrick 21 
states that the Domesticas and Insititias grow most satisfactorily on rich 
clay loams, while the Trifloras, Hortulanas and Munsonianas give best 
results on light soils. These group names, however, represent distinct 
species and consequently differences greater than those usual between 
varieties of the same kind of fruit. 

Wilder, 66 who has made a special study of the fruit soils of southern New 
England, makes the following statements regarding the special soil requirements 
of certain well known apple varieties: "Soils grading from medium to semi-light 
fulfill the best requirements of the Baldwin. This grouping would include the 
medium to light loams, the heavy sandy loams, and also the medium sandy loams, 
provided they were underlaid by soil material not lighter than a medium loam 
nor heavier than a light or medium clay loam of friable structure." From this 
broad generalization it will be seen that the surface soil should contain an ap- 
preciable amount of sand. The sands, moreover, should not be all of one grade, 



670 FUNDAMENTALS OF FRUIT PRODUCTION 

that is, a high percentage of coarse sand would give a poor soil, whereas a moderate 
admixture of it with the finer grades of sand, together with sufficient clay and 
silt, would work no harm. 

"A surface soil of heavy, siity loam or light, silty, clay loam underlain by 
silty clay loam excells for the 'green' Rhode Island Greening. Such soil will 
retain sufficient moisture to be classed as a moist soil, yet it is not so heavy as 
ever to be ill drained if surface drainage is inadequate. The soil should be 
moderately rich in organic matter, decidedly more so than for the Baldwin. 
Such soil conditions maintain a long seasonal growth under uniform conditions 
of moisture, and thus produce the firm yet crisp texture, the remarkable juiciness 
and the high flavor for which this variety is noted when at its best. If grown on 
a soil too sandy, the Rhode Island Greening lacks fineness of grain, flavor and the 
juicy quality in greater or lesser degree, depending on the extent of the departure 
from those soil characteristics which contribute to its production. 

"This variety [Northern Spy] is one of the most exacting in soil requirements. 
To obtain good quality of fruit, i.e., fine texture juiciness and high flavor, the 
soil must be moderately heavy, and for the first two qualities alone the Rhode 
Island Greening soil would be admirable. The fact that the Northern Spy is a 
red apple, however, makes it imperative that the color be well developed and the 
skin free from the greasy tendency. This necessitates a fine adjustment of soil 
conditions, for the heaviest of the soils adapted to the Rhode Island Greening 
produces Northern. Spies with greasy skins and usually of inferior color. Its 
tendency to grow upright seems to be accentuated by too clayey soils, if well 
enriched and such soils tend to promote growth faster than the tree is able to 
mature well. On the other hand, sandy soils, while producing good color and 
clear skins, fail to bring fruit satisfactory in quality with respect to texture and 
flavor. The keeping quality, too, is inferior to that of the Spy grown on heavier 
soils in the same district. Hence the soil requirements of this variety are de- 
cidedly exacting, and are best supplied apparently by a medium loam underlain 
by a heavy loam or light clay loam. It should not be planted on a soil lighter 
than a very heavy, fine, sandy, loam, underlain by a light clay loam, or possibly a 
heavy loam. On light soils the Nothern Spy very often yields less per acre 
than the Baldwin. 

"Both Ben Davis and Gano show less effect from variation in the soils upon 
which they are grown than any others observed." 

In speaking of the special soil requirements of peach varieties the same author 
has this to say: 

"Judging from the experience of a very large number of growers in Connecti- 
cut and in other States, combined with field observations, it seems evident that 
the Champion peach is especially sensitive to any condition of subsoil which 
hinders the ready movement of moisture within a probable depth of as much as 
4 feet from the surface. Carman and Mountain Rose are not quite so dependent 
as the Champion on soils that drain out hastily, and while they succeed best on 
soils of a little greater moisture-holding capacity than the Champion, they never- 
theless give the best results on deep and well-drained soils. The Elberta and 
the Belle thrive on well-drained soils that are somewhat stronger than the varie- 
ties previously mentioned." 67 



ORCHARD SOILS 671 

There is some reason to believe that the importance of these variety 
preferences is often overemphasized. For instance to assert that the 
Yellow Newtown (Albemarle Pippin) apple will do well only on the so- 
called "pippin" soils of Virginia and North Carolina is to misstate the 
facts, except perhaps for the soils of those particular states. The variety 
does equally well on quite different soils in the Hudson River, Hood 
River and Rogue River valleys and in New South Wales, though on these 
other soils it may develop a slightly different but in no way inferior, 
shape, color or flavor. Some of the variation in the chemical composition 
of fruits is without doubt due to diversities in soil and in some parts of 
the world these differences are regarded as of considerable importance 
in the production of grapes for wine; however, much of the variation in 
composition is due to other factors of environment, such as temperature, 
sunlight and humidity. Their influence must be subtracted before it 
can be said that the difference in the quality of fruit from two different 
sections, or even orchards, is due to soil variation. Nevertheless, the 
ways in which soil influences the development of individual varieties may 
well be studied, for often the information gained can be of much use in 
actual fruit production. For instance, if a piece of land that is to be 
planted to apple trees includes some light and some heavy soil and two 
varieties, one a red and the other a yellow apple, are to be set, it will 
generally be wise to plant the red variety on the lighter soil and the 
yellow variety on the heavier, so far as possible. Though soil probably 
exerts very little, if any, direct influence on pigment production 
in the fruit, the type of vegetative growth obtained on the lighter soil 
is likely to permit and encourage higher coloration of the fruit than that 
obtained on the finer textured land. 

It is easier to modify through treatment the chemical condition of the 
soil than its physical condition and obviously, it is generally easier to 
modify surface soil than subsoil. The subsoil must be taken largely as 
it is found. Consequently in selecting a piece of land for fruit growing 
the subsoil should be given specially careful consideration, particularly 
as regards its physical condition. Both physical and chemical condition 
of the surface soil may be modified materially, but to effect any consider- 
able change, particularly in physical character, is expensive. The grower 
should never forget that the business must yield a fair return on the 
investment. 

Summary. — In general fruit crops demand the same qualities in a 
soil as cereal or forage plants. On account of their growing habits, 
however, depth of soil, character of subsoil and general physical condition 
are of relatively greater importance to the former. Different fruit crops 
show varying adaptation to soils of quite dissimilar textures. Practically 
all, however, are alike in requiring considerable depth, thorough aeration 
and freedom from hardpan, plowsole or other impervious strata. It is 



672 FUNDAMENTALS OF FRUIT PRODUCTION 

impracticable at present to attempt a definition of the soil requirements 
of different fruit plants in terms of mechanical analysis. 

Soils that are unproductive from the standpoint of cereal crops are 
often productive from the standpoint of fruit production and the reverse 
situation often occurs. It is even more impracticable to attempt a defini- 
tion of the soil requirements of different fruits in terms of chemical compo- 
sition, than in terms of mechanical analysis. The character of the vegeta- 
tion growing naturally on a soil furnishes one of the best indices to the 
kinds of fruit that may be expected to thrive on it. Though there are 
indications of marked adaptation of particular varieties to certain soil 
types, the importance of such special adaptations is often exaggerated. 

Suggested Collateral Readings 

Batchelor, L. D., and West, F. L. Variation in Minimum Temperatures Due to the 

Topography of a Mountain Valley in its Relation to Fruit Growing. Utah Agr. 

Exp. Sta. Bui. 141. 1915. 
Wickson, E. J. California Fruits: How to Grow Them. Pp. 27-37. San Francisco, 

1910. 
Russell, E. J. Soil Conditions and Plant Growth. Chapters 3 and 8. Pp. 52-79; 

153-169. London, 1915. 
Bowman, I. Forest Physiography. Pp. 27-40, 107-126. New York, 1914. 

Literature Cited 

1. Abbe, C. U. S. D. A., Mo. Weather Rev. 21. 1893. Cited by Garriot, E. B 

U. S. D. A. Farmers' Bui. 104. 1899. 

2. Batchelor, L. D., and West, F. L. Utah Agr. Exp. Sta. Bui. 141. 1915. 

3. Bigelow, F. H. U. S. D. A., Weather Bur. Bui. R. 1908. 

4. Cal. Agr. Exp. Sta. Bui. 25. 1884. 

5. Cal. Agr. Exp. Sta. Rept. for 1894-95. P. 15. 1896. 

6. Cal. Agr. Exp. Sta. Ann. Rept. 1903-1904. 

7. Coville, F. V. U. S. D. A., Bur. PI. Ind. Bui. 193. 1910. 

8. Finch, C, and Baker, D. O. Geography of the World's Agriculture. U. S. D. A., 

Office Farm Management. 1917. 

9. Fliche, P., and Grandeau, L. Ann. Chem. et Phys. ser. 5. 2: 354-379. 1874. 

10. Forbes, R. H. Ariz. Agr. Exp. Sta. Bui. 28. 1897. 

11. Fritz, H. Intern, wissensch. Bibliothek, Band 68. Leipzig, 1889. Cited by 

Abbe, C. U. S. D. A., Weather Bur. Bui. 36. 1905. 

12. Gager, C. S. J. N. Y. Bot. Garden 8. 1909. Cited in U. S. D. A., Mo. 

Weather Rev. 36: 63. 1908. 

13. Georgeson, C. C. Alaska Agr. Exp. Sta. Ann. Rept. P. 9. 1906. 

14. Ibid. P. 21. 1907. 

15. Ibid. P. 20. 1908. 

16. Ibid. Pp. 8, 9. 1909. 

17. Green, W. J. Ohio Agr. Exp. Sta. Bui. 137. 1903. 

18. Hann, J. Handbuch der Klimatologie. Stuttgart, 1911. 

19. Hedrick, U. P. Grapes of New York. Pp. 131, 152. Albany, 1908. 

20. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 314. 1909. 

21. Hedrick, U. P. Plums of New York. P. 113. Albany, 1911. 

22. Heyer, G. Forstl. Bodenk. u. Klimatol. P. 488. 1856. Cited in Nisbet, J. 

Studies in Forestry. P. 53. Oxford, 1894. 



GEOGRAPHIC INFLUENCES 673 

23. Higgins, J. E. Hawaii Agr. Exp. Sta. Bui. 7. 1904. 

24. Higgins, J. E., and Holt, V. S. Hawaii Agr. Exp. Sta. Bui. 32. 1914. 

25. Hilgard, E. W. Cal. Agr. Exp. Sta. Rept. for 1890. P. 41. 1891. 

26. Hilgard, E. W. Cal. Agr. Exp. Sta. Rept. for 1892-3. P. 328. 1894. 

27. Hilgard, E. W. Cal. Agr. Exp. Sta. Rept. for 1897-1898. P. 41. 

28. Hilgard, E. W. Soils, 6th ed. P. 182. 1914. 

29. Hodgson, R. W. Cal. Agr. Exp. Sta. Bui. 276. 1917. 

30. Hopkins, C. G. Soil Fertility and Permanent Agriculture. P. 69. 1910. 

(Computed from his data.) 

31. Husmann, G. C. U. S. D. A., Bur. PI. Ind. Bui. 172. 1910. 

32. Jaffa, M. E. Cal. Agr. Exp. Sta. Rept. for 1892-3. P. 238. 1894. 

33. Johnson, M. O. Hawaii Agr. Exp. Sta. Press Bui. 51. 1916. 

34. Kearney, T. H. U. S. D. A. Bur. PL Ind. Bui. 125. 1908. 

35. Kedzie, R. C. Mich. Agr. Exp. Sta. Bui. 99. 1893. 

36. Kelley, W. P. Hawaii Agr. Exp. Sta. Bui. 26. 1912. 

37. Kerner, A., and Oliver, F. W. Natural History of Plants. 1 (2) : 528. New 

York, 1895. 

38. King, F. A. Wis. Agr. Exp. Sta. Ann. Rept. 12: 268-272. 1895. 

39. Kinman, C. F. Porto Rico Agr. Exp. Sta. Bui. 24. 1918. 

40. Lippincott, J. S. U. S. Rept. Com. Agr. Pp. 137-190. 1866. 

41. Loughridge, R. H. Cal. Agr. Exp. Sta. Bui. 133. 1901. 

42. Mac Dougal, D. T. Mem. Hort. Soc. N. Y. 2: 3-22. 1907. 

43. Mason, S. C. U. S. D. A. Bui. 271. 1915. 

44. Mass. St. Board of Agr., Ann. Rept. 59: 14-15. 1911. 

45. Merriam, C. H. U. S. D. A., Div. of Biol. Surv. Bui. 10. 1898. 

46. Miller, H. K., and Hume, H. H. Fla. Agr. Exp. Sta. Bui. 68. 1903. 

47. Ney. Lehre von Waldbau. P. 64. 1885. Cited in Nisbet, J. Studies in 

Forestry. Oxford, 1894. 

48. Persons, A. A. Fla. Agr. Exp. Sta. Bui. 43. 1897. 

49. Riviere, G., and Bailhache, G. Prog. Agr. et Vit. 53 (15): 453-454. 1910. 

50. Shaw, G. W. Ore. Agr. Exp. Sta. Bui. 50. 1898. 

51. Shreve, F. Cam. Inst. Wash. Pub. 217. 1915. 

52. Stewart, J. P. Pa. Agr. Exp. Sta. Bui. 153. 1918. 

53. Thatcher, R. W. Wash. Agr. Exp. Sta. Bui. 85. 1908. 

54. U. S. D. A., Bur. Soils, Bui. 5. 1896. 

55. U. S. D. A., Operations Div. Soils for 1900. P. 303. 1901. 

56. Ibid, for 1901. P. 464. 1902. 

57. Ibid, for 1904. P. 1127. 1905. 

58. Ibid, for 1905. P. 959. 1907. 

59. Ibid, for 1909. P. 1721. 1921. 

60. Vinson, R. S., and Russell, E. J. J. Agr. Sci. 2: 225. 1907. 

61. Vosbury, E. D. U. S. D. A. Farmers' Bui. 1122. 1920. 

62. Wheeler, H. J. U. S. D. A. Farmers' Bui. 77. 1905. 

63. Whitney, M. U. S. D. A., Bur. Soils, Bui. 13. 1898. 

64. Wilcox, E. V. Tropical Agriculture. Pp. 2, 5. 1916. 

65. Ibid. P. 19. 1916. 

66. Wilder, H. J., Mass. St. Board Agr. Ann. Rept. 59: 13-23. 1911. 

67. Wilder, H. J. U. S. D. A. Bui. 140. 1915. 



43 



674 FUNDAMENTALS OF FRUIT PRODUCTION 

GLOSSARY 

Adiabatic. — A curve exhibiting variations of pressure and volume of a fluid when 

it expands without receiving or losing heat. 
Adsorption. — The adhesion of molecules of gases or dissolved substance to the sur- 
faces of solid particles; distinguished from absorption, which is not a surface 
phenomenon. 
Aitionomic. — As referred to parthenocarpy, the ability to develop parthenocarpic 

fruits only in response to some stimulus external to the ovary. 
Akene. — Dry, unilocular, indehiscent fruit, seed-like in appearance, as in the straw- 
berry. 
Alkali. — (1) In chemistry, a base; (2) as applied to soils, salts present in amounts 
harmful to plants, chiefly sodium chloride, sodium sulfate and sodium 
carbonate. 
Antagonism. — Of salts, a mutual counteraction of their influence on cell permeability. 
Arginine. — A basic amino-acid which is a product of protein digestion. 
Autocatalysis. — A process of catalysis where the catalytic agent is an end product 

of the reaction catalyzed. 
Autogamy. — When a flower is fertilized by its own pollen. 
Autonomic. — As referred to parthenocarpy, the ability to set fruit without the 

stimulus resulting from pollination. 
Barren. — Unproductive. 

Breba. — One of the crops of the pistillate fig tree, the first to mature in the spring. 
Caprifig. — The wild or "male" fig, the uncultivated form. 
Chemotropism. — A bending or turning in response to a chemical stimulus. 
Chlorosis. — A diseased condition shown by loss of green color. 
Choline. — An amine arising as one of the products of lecithin decomposition. 
Colloid. — A state of a substance where the units are very large molecules or molecule 
complexes. Colloids diffuse slowly or not at all through plant or animal mem- 
branes. 
Compatibility. — (1) Of sex cells, the ability to unite and form a fertilized egg that 
can grow to maturity. (2) Congeniality as determined by the degree of success 
of the union between stock and cion. 
Coulure. — The failure of blossoms to set, resulting in a premature drop. Cf. 

millerandage. 
Court-noue. — A physiological disturbance of the grape manifested by short nodes. 
Creatine. — A nitrogenous compound readily converted into creatinine. 
Creatinine. — A basic nitrogenous compound occuring naturally in muscle tissue and 

urine. 
Cumarine. — An organic compound with vanilla-like odor known as tonka bean 

camphor. 
Dichogamy. — Insuring cross fertilization by the sexes being developed at different 

times. 
Dicliny. — Male and female organs separate and in different flowers. 
Dihydroxy -stearic Acid. — A double hydroxide of a common fatty acid. 
Dimorphism. — Presenting two forms, as long and short growths or permanent and 

deciduous branches. 
Dioecious. — Unisexual, the male and female elements in different individuals. 
Disaccharide. — A compound sugar yielding two simple sugars on hydrolysis. 
Dormant. — Applied to buds when they are not actively growing and to plants when 

they are not in leaf. 
Emasculation. — The artificial removal of the stamens from the flower before they 
dehisce. 



GLOSSARY 675 

Embryogenic. — Pertaining to the development of the embryo. 

Embryo Sac. — The cell in the ovule in which the embryo is formed. 

Endocarp. — The inner layer of the wall of a fructified ovary. 

Endosperm. — The nutritive material stored within a seed, originally deposited within 

the embryo sac. 
Exocarp. — The outer layer of the wall of a fructified ovary. 
Extine. — The outer coat of a pollen grain. 

Fasciation. — A diseased condition resembling the growth of several stems into one. 
Fecundation. — The fusion of two gametes to form a new cell. 
Fecundity. — The ability of flowers to produce seeds that will germinate. 
Fertility. — (1) Of flowers, the capacity of producing seeds that will germinate; (2) 

of soils, the crop producing power. 
Fertilization. — (1) The fusion of two gametes to form a new cell; (2) the application of 

fertilizers. 
Frenching. — A disease characterized by loss of color in leaves between the veins. 
Fruitfulness. — The capacity of producing fruit. 
Fruit Setting. — A development of the ovary and adjacent tissues following the 

blossoming period. 
Gamete. — A unisexual cell which must fuse with another gamete to produce a new 

individual. 
Glucosides. — Compounds that yield sugar and some other substance, usually aro- 
matic, on hydrolysis. 
Guanine. — A basic nitrogenous compound related to uric acid; one of the purines. 
Gynaeceum. — The pistil or pistils of a flower. 
Hermaphrodite. — A flower with both stamens and pistils. 

Heterostyly. — The presence of styles of two or more forms or two or more lengths. 
Heterotypic. — Reduction division of a cell. 

Histidine. — A basic amino-acid which is a product of protein digestion. 
Homotypic. — As applied to cell division, involving the usual process of karyokinesis. 
Hydrolysis. — Chemical splitting by taking up the elements of water. 
Hygroscopic Coefficient. — The percentage of soil water retained in contact with a 

saturated atmosphere and in the absence of any other source of moisture. 
Hypoxan thine. — A basic nitrogenous compound related to uric acid; one of the 

purines. 
Imbibition. — The process of absorption, usually by a solid. 
Imperfect. — In flowers, unisexual. 
Impotence. — Inability to produce functional gametes of the one sex or the other; 

sometimes used in a more general sense to denote sterility. 
Incompatibility. — Of sex cells, the inability to unite and form a fertilized egg that can 

grow to maturity. 
Interfertility. — The ability of one variety to set fruit and produce seeds that will 

germinate when pollenized by another variety. 
Interfruitfulness. — The ability of one variety to set and mature seed-containing or 

seedless fruit when pollenized by another variety. 
Intersexualism. — Sex intergrades; a term referring to the varying degrees of develop- 
ment of the two sex organs in the same plant; relative maleness or femaleness 

of the plant. 
Intersterility. — Inability of one variety when pollenzied by another variety to set 

fruit and produce seeds that will germinate. 
Intine. — The inner coat of a pollen grain. 
June Drop. — The abscission of partly developed fruit (often occurring in June). 



676 FUNDAMENTALS OF FRUIT PRODUCTION 

Latent Bud. — A bud, usually concealed, more than one year old, which may remain 

dormant indefinitely or may develop under certain conditions. 
Lecithin. — A fat-soluble compound containing nitrogen and phosphorus. 
Locule. — The cavity of an anther or ovary. 
Mamme. — One of the crops of the caprifig or "male" fig, the first to mature in the 

spring. The fruits of this crop winter over as comparatively large specimens. 
Mammoni. — One of the crops of the caprifig or "male" fig, which sets in June and 

matures in late summer. 
Millerandage. — A condition in the grape where the ovary persists but the seeds 

remain small or do not attain usual size; produced by conditions similar to those 

that lead to coulure. 
Monoecious. — The stamens and pistils in separate flowers but borne on the same 

individual. 
Nucleic Acid. — Phosphorus-containing acids, usually combined with protein in all cell 

nuclei. 
Nucleins. — Phosphorus-containing compounds of nucleic acid with protein. 
Osmosis. — Diffusion through a membrane. 

Parthenocarpy. — The production of fruit without true fertilization. 
Parthenogenesis. — The development of the unfertilized egg into the usual product of 

fertilization without a preceding union of gametes. 
Pedicel. — The support of a single flower of an inflorescence. 
Peduncle. — The support of an inflorescence or a flower stalk. 
Pentosan. — A polysaccharide that yields five-carbon sugars on hydrolysis. 
Perennation. — A lasting state, referring particularly to the persistance of fruit long 

after its usual season of maturity. 
Perfect. — Hermaphrodite flowers. 
Picoline. — A basic derivative of pyridine. 
Pollination. — The placing of pollen on the stigmatic surface. 
Pollinium. — A pollen mass consisting of all the pollen grains of an anther locule. 
Polyembryony. — The production of more than one embryo in an ovule. 
Polygamo-dioecious. — With hermaphrodite and unisexual flowers on different 

individuals of the same species. 
Polygamous. — With hermaphrodite and unisexual flowers. 
Polysaccharide. — A carbohydrate which yields a large but indefinite number of 

simple sugars on hydrolysis; usually colloids. 
Polyterpenes. — Compounds which yield an indefinite number of simple hemiterpene 

units on distillation; ex. caoutchouc, balata. 
Profichi. — One of the crops of the caprifig or "male" fig, the second to mature in the 

spring. The fruits of this crop appear as small buttons in the late fall or early 

winter. 
Proliferation. — A rapid and repeated production of new parts, as the formation of 

leafy parts from floral parts. 
Protandry. — The pollen being discharged before the pistils are receptive. 
Protogyny. — The pistils receptive before the anthers have ripe pollen. 
Pseudo-hermaphrodite. — Functional unisexuality in the presence of apparently well 

developed stamens and pistils. 
Purines. — A group of nitrogenous organic compounds such as uric acid, xanthine and 

caffein. 
Pyridine. — A nitrogenous base which is the nucleus of many organic compounds, for 

example nicotine. 
Pyrimidines. — A group of basic nitrogenous compounds related to the purines and 

found as products of nucleic acid cleavage. 
Quinone. — An oxidation product of benzene. 



GLOSSARY 677 

Respiration. — Gaseous exchange by which the plant absorbs oxygen and gives off 

carbon dioxide. 
Respiratory Coefficient. — The amount of carbon dioxide given off divided by the 

amount of oxygen used in respiration. 
Salicylic Aldehyde. — An oxidation product of salicin giving the fragrance to 

meadow-sweet. 
Somaplasm. — The protoplasm other than the germplasm. 

Sod Culture. — A method of orchard soil management in which a permanent perennial 
crop is grown between the trees, mowed once or twice during the growing season 
and then allowed to remain on the ground. A limited area around the trees is 
hoed, spaded or otherwise tilled. 
Sod Mulch. — A method of orchard soil management in which a permanent perennial 
crop is grown between the trees, mowed once or twice during the growing season 
and then allowed to remain on the ground. 
Sporogenous. — Producing spores. 
Sporophyte. — The plant in the alternating life cycle arising from a fertilized egg and 

producing spores. 
Sterility. — The inability to produce seeds that will germinate. 
Supercooling. — Cooling below the freezing point without solidification. 
Temperature Inversion. — A rise in temperature with increasing distance from the 

ground, up to a certain height. 
Tetrad. — A group of four cells such as the pollen grains derived from one spore mother 

cell. 
Torus. — (1) The receptacle of a flower, part of the axis on which the flower parts are 

inserted; (2) the thickening in the center of the membrane in bordered pits. 
Trimorphism. — Heterogomy, or with long-, short-, and mid-styled flowers. 
Vacuole. — In cells, the cell sap surrounded by protoplasm. 
Vanillin. — An aromatic compound, the fragrant constituent of vanilla. 
Wilting Coefficient. — The percentage of moisture in the soil when permanent wilting 

of plants takes place. 
Xanthine. — A basic nitrogenous compound related to uric acid; one of the purisen. 
Xenia. — The direct influence of foreign pollen on the part of the mother plant that 
develops into endosperm. 



INDEX 



(Principal discussions are in bold face type) 



Abortion, embryo, 626-626 

embryo sac, 495, 514, 521 

ovary, 487 

pistil, 484, 495, 504, 507, 511 

pollen, 478, 496-498, 507, 511-514 
Absorption, 18-22 

nitrogen, 130 

relation to concentration, 105 

relation to transpiration, 127 

selective, 126 
Acclimatization, 241 
Acidity of soil, see Soil Reaction. 
Acid tolerance of fruits, 118, 226 
Adsorption, 49, 266-260 
Aeration of soil, 126 
Age and fruit setting, 614 
Air drainage, 346-349, 643-662 
Alkali, see Concentration, Soil Reaction. 
Almond, composition, 101, 138, 144, 149, 152, 
156, 160 

frost injury, 359 

fruit-bud formation, 187 

fruiting habits, 402 

fruit setting, 500, 542 

geography, 621 

pruning, 465 

soils, 657 

stocks, 553, 559, 564, 587, 601 

varietal differences, 542 

water requirements, 3, 16 

winter injury, 291 
Alternate bearing, see Fruiting Habits. 
Altitude, 621 

see Elevation. 
Aluminum, in plant tissues, 160 

in soils, 663-665 
Ammonium, 106 
Antagonism, 126 
Antipodals, 477 

Apple, composition, 4, 5, 102-104, 133-138, 141- 
158, 254, 275, 319, 320 

cultivation, 66, 71, 77 

fertilizers, 206-217 

frost injury, 359-362, 364, 381 

fruit-bud formation, 186-192 

fruit development, 530, 531, 534 

fruiting habits, 399, 457-461 

fruit setting, 500, 503-505, 509, 511, 518, 
521, 531, 640 

geography, 612, 614, 619-620, 624-628 

irrigation, 71, 73 

physiological disturbances, 79, 83, 88-96 

propagation, 689-696 



679 



Apple, pruning, 408-433, 439-447, 450-453, 467- 
461 

root distribution, 66-61, 581 

soils, 660-662, 666, 668-670 

stocks, 312, 316, 553-554, 558-559, 562, 
565-567, 571-578, 581, 588-592, 599, 
601 

temperature requirements, 238-248, 624-628 

varietal and group differences, 86, 190, 207, 
242-244, 254, 271, 319-322, 362, 422- 
424, 430, 441-443, 540, 581, 588, 594, 
624-626, 669 

water requirements, 3, 7, 16 

winter injury, 255-256, 261, 267-271, 279, 
291, 304, 312, 318-322 
Apricot, composition, 138, 144, 149, 156 

frost injury, 359-360 

fruiting habits, 402 

fruit setting, 519, 543 

geography, 621 

physiological disturbances, 95 

pruning, 465 

stocks, 556, 575 

temperature requirements, 245 

water requirements, 3, 8, 16, 16 

winter injury, 291 
Arsenical poisoning, 196 
Aspect, see Slope. 
Assimilation, 161-166 
Atmospheric humidity, see Humidity- 
Autogamy, 480 
Availability, 107-108 

iron, 109, 116-117 

nitrogen, 109 

phosphorus, 108, 116 

sulfur, 109 

water, 16, 47-49 
Axial row, 477 
Azarole, see Hawthorn. 



B 



Bark splitting, 300 

Barrenness, see Fruitfulness. 

Bearing habits, see Fruiting Habits. 

Biennial bearing, see Regularity of Bearing. 

Bitter-pit, 93, 195, 197 

Blackberry (and Dewberry), composition, 4, 150 

fertilizers, 207 

fruit-bud formation, 188 

fruiting habits, 402, 467 

fruit setting, 498-500, 544 

geography, 626, 634 

pruning, 453, 467 

soils, 118 



680 



INDEX 



Blackberry, varietal and group differences, 332- 
336, 498 

winter injury, 315, 332-336 
Black-end, 94 

Blossoming season, 342-346, 365-369 
Blueberry, fruit-bud formation, 403 

geography, 618 

soils, 118, 657, 662 



Calcium, antagonism, 126 

deficiencies, 199 

displacement, 106 

in fertilizers, 110, 157, 201-202, 221, 226 

and nitrification, 110 

in organic compounds, 154 

in plant tissues, 101-104, 127, 154-166 

relation to chlorosis, 116 
in soils, 156-157, 222, 663-665 
Carbohydrates, 167-168 

in plant tissues, 167, 171-176 

relation to fruit-bud formation, 181-185 

relation to pigment formation, 180 

storage, 170, 182-183 

synthesis, 167 

translocation, 167-176, 199, 434-435, 451 

utilization, 176-180, 184, 199, 451 
Carbon assimilation, 162-166 
Carotin, 164 
Chalaza, 477 

Cherry, composition, 4, 102-103, 132-133, 138, 
140-141, 144-146, 149-150, 154-156 

frost injury, 359-360 

fruit-bud formation, 188 

fruiting habits, 401, 464 

fruit setting, 486, 500-501, 543 

geography, 612, 620-621, 626 

physiological disturbances, 95 

pruning, 410, 464-466 

root distribution, 62 

stocks, 248, 313, 553-554, 560, 562, 566, 568, 
582, 585 

temperature requirements, 326, 628 

varietal and group differences, 313, 326-328, 
401, 486, 543 

water requirements, 8, 16 

winter injury, 288, 291, 297-298, 313, 326- 
328 
Chestnut, composition, 4, 101, 102, 138, 144, 149, 
152, 153, 156, 158 

fruiting habits, 404 

stocks, 570 

winter injury, 292 
Chinquapin, see Chestnut. 
Chlorine, 159, 199 
Chlorophyll, 164-165 
Chlorosis, 85, 116-117, 199, 569, 662 
Cion, influence on stock, 579-583 

rooting, 594 

selection, 603-606 
Citrus fruits, composition, 150, 152 

geography, 621 

physiological disturbances, 106, 116, 120 

propagation, 590, 596 

soils, 660, 669 



Citrus fruits, stocks, 582, 587 

water requirements, 3 

winter injury, 272 

see Orange. 
Climate, see Temperature, Winter Injury, 

Precipitation. 
Clouds and frost, 341 
Concentration of sap, see Sap Density. 
Concentration of soil solution, injuries from 
"alkali," 119-121, 196 

requisites for absorption, 105 

and root distribution, 64 

tolerance of different plants, 118-119 
Congeniality of grafts, 652-557 
Copper poisoning, 195 
Cork, 89 

Coulure, 454, 497, 514 
Cover crops, acid tolerance, 118 

and nitrogen fixation, 114-115 

and soil moisture, 34-35, 41-46, 279-281 

and soil temperature, 307 

toxic action, 124 

and winter injury, 271, 279-281, 310-312 
Cranberry, 85, 188, 202, 349-356, 618 
Cross sterility, 501 
Crotch and crown injury, 271-274 
Cultivation, 31, 38-39 

and frost danger, 355 

and fruit setting, 81 

and nitrification, 111-114 

and root distribution, 63 

an I run-off, 32 

and soil temperature, 306-307 

and vegetative growth, 66 

and water requirement, 10 

and winter injury, 269, 270, 279, 289 
Cup-shake, 300 
Currant, composition, 4, 150, 258 

fruit-bud formation, 188 

fruiting habits, 402 

fruit setting, 544 

geography, 618 

physiological disturbances, 84 

pruning, 466 

temperature requirements, 628 

varietal and group differences, 335, 466 

winter injury, 315, 335 
Cuttings, propagation by, 589-595 



Date palm, 242, 487 

Defoliation, 86 

see Summer Pruning. 

Degeneration, see Abortion. 

Dehorning, 427-429 

Depth of freezing, see Soil Temperature. 

Depth of rooting, see Root Distribution. 

Dewberry, see Blackberry. 

Dewpoint and frost, 341, 370 

Dieback, 88, 91-92, 195 

Dioecious plants, 490-492 

Disease, extent of injury, 2 
fruit setting, 518 
susceptibility, 75, 568-569 



INDEX 



681 



Disease, see Parasites, Physiological Disturbances. 

Displacement, 106 

Distance of planting, see Planting. 

Double fertilization, 477, 482 

Double working, 601-603 

Drought injury, 2, 14-16, 41, 86-95, 257, 274 

Dwarfing, 432-434, 557-560, 575, 579-580, 597 



E 



Egg apparatus, 477 

Elder, 400 

Elevation, 339, 346-351, 643-648 

Embryo, abortion, 525-526 

formation, 482 
Embryo sac, 477 
Endosperm, 482 
Enzymes, 166 

Evaporation, 45, 281-282, 654 
Exanthema, see Dieback 
Exposure, see Slope. 



False-blossom, 85 
Fasciation, 84, 416 
Fertility, 487, 506, 510 

see Fruitfulness, Fruit Setting. 
Fertilization, 481 
Fertilizers, 151, 222-225 

excessive applications, 119 

fruit setting, 510 

indirect effects, 218-221 

lime, 221 

methods of action, 200 

nitrification, 110 

nitrogenous, 204-217, 510 

orchard requirements, 200-203, 667 

phosphorus, 218-219 

protective action, 123 

soil temperature, 307 

sulfur, 219, 226 

time of application, 227-228 

water requirement, 10, 12 

winter injury, 289 
Fig, composition, 138, 144, 149, 156, 158 

fruit development, 533-534 

fruiting habits, 404 

fruit setting, 491, 493, 513, 623-524 

geography, 621 

physiological disturbances, 83 

water requirements, 3, 16 
Filbert, 188, 403, 493 
Frenching, 106 

Freeze and frost distinguished, 338 
Frost, crack, 298-300 

danger, 342-366, 366 

formation, 337-341, 351, 370 

injury; 2, 358-365, 380-381 

penetration, see Soil Temperature. 

prediction, 369-373 

protection, 373-380 
Fruit-bud formation, 181-193, 413-414, 419-425, 

451-452, 570-572 
Fruit development, 525, 629-636 



Fruitfulness, 487 

age and vigor, 614 
compatibility, 500-502, 507 
dichogamy, 492-494, 512 
evolutionary tendencies, 489-498 
external factors, 509-520 
genetic factors, 489, 498-502 
grafting, 510 
heterostyly, 492 
hybridity, 499 
intersexualism, 490-492 
locality, 510-512 
moisture supply, 516 
nutrient supply, 509 
nutritive conditions, 504-607 
physiological factors, 489, 502-507 
pistil abortion, 494-495, 507 
pollen abortion, 496-498, 507, 512 
pollen tube growth, 481, 602 
season, 512-514 
temperature, 614-516 
time of pollination, 503 

Fruiting habits, 397-406 

Fruit-pit, 89, 93 

Fruits classified, 475 

Fruit setting, 483, 487 
disease, 518 

humidity, 80-82, 516-517 
individual fruits, 540-545 
June drop, 484-487 
nitrogenous fertilizers, 209-211 
pinching, 454 
ringing, 436 
spraying, 519 

stimulating agents, 521-525 
wind, 518 

Fruit splitting, 81 

Fruit zones, 612-621 

Funicle, 477 



G 



Girdling, see Ringing. 
Gooseberry, composition, 4, 150 

fruit-bud formation, 188 

fruit development, 529-530 

fruiting habits, 402 

fruit setting, 544 

geography, 618 

pruning, 466 

stocks, 553, 568 

temperature requirements, 243, 248, 628 

winter injury, 315, 335 
Grafting, 652-567, 600 
Grape, composition, 4, 138-139, 143-144, 152-159 

coulure, 454, 457, 5l9, 572 

fertilizers, 226 

frost injury, 359 

fruit-bud formation, 188 

fruit development, 532 

fruiting habits, 402, 468 

fruit setting, 436, 484, 496-499, 502, 509- 
514, 518, 521, 543, 572 

geography, 612, 615-616, 620-624, 633 

irrigation, 330 

millerandage, 572 



682 



INDEX 



Grape, physiological disturbances, 80, 86-87, 
117, 569 

pinching, 454 

propagation, 591 

pruning, 438, 453-454, 467-471 

ringing, 436 

root distribution, 582, 591 

soils, 658-662, 668 

stocks, 553, 555, 559, 560, 563-582, 586-588 

temperature requirements, 241-247, 623-624 

training, 470 

varietal and group differences, 244, 314, 330, 
331, 470, 496, 526, 543 

water requirements, 3, 16 

winter injury, 314, 329-331 
Gummosis, 568 



II 



Hail injury, 2 

Hardiness, see Frost Injury, Winter Injury, 

Winter Killing. 
Haw, 400 
Hawthorn, 400 
Heading back, see Pruning. 
Heating, see Orchard Heating. 
Heat units and requirements, 236-247 
Heeling-in, 19 
Heterostyly, 492, 502 
Hickory, 405, 620 
Humidity, fruit setting, 80-83, 516 

geography of fruit production, 631 

growth, 78-82 

russeting, 79 

winter injury, 274 
Hybridity and unfruitfulness, 499 
Hygroscopic coefficient, 13 



Immaturity, see Winter Injury, Winter Killing. 

Impotence, 478, 494-498 

Incompatibility, fruitfulness, 500-602, 507, 511 

grafts, 662-567 
Integuments, 477 

Interfertility, see Fertility, Fruitfulness. 
Intercrops, 40-41, 81, 124 
Interfruitfulness, 501 
Intersexualism, 490-492, 499 
Inversion of temperature, see Temperature 

Inversion. 
Iron, availability, 109, 116-117 

deficiencies, 116, 199 

in fertilizers, 117, 668 

in plant tissues, 101, 151-162 

in soil, 663-665 

solubility, 152 
Irregular bearing, see Regularity of Bearing. 
Irrigation, 8 

"alkali," 121 

color and quality of fruit, 74-75 

frost danger, 354 

fruit size, 71 

vegetative growth, 66 

winter injury, 278, 335 



Jonathan spot, 93 

Jujube, 404 

Juneberry, 400 

June drop, see Fruit Setting. 



K 



Killing back, 268-271 
see Dieback. 



Land values, 638 
Latitude, 237-239, 342-343 

Layering, 593 

Leaf pigments, 164 

Light, carbohydrate manufacture, 183 

frost injury, 262 

fruit-bud formation, 183 

fruit setting, 516 

nitrogen elaboration, 130 

phosphorus elaboration, 138 

transpiration, 27 

water requirement, 11 
Lime, see Calcium. 
Lithiasis, 95 
Location, frost danger, 342-346 

fruit setting, 510-512, 515 

selection of, 635, 637-639 
Loquat, 399, 553, 564, 575, 621 

M 

Macrosporangium, 473 
Macrospore, 477 
Magnesium, antagonism, 126 

deficiencies, 199 

displacement, 106 

excesses, 195 

in plant tissues, 101-102, 162-153 

in soil, 663-665 
Manure, see Fertilizers. 
Manganese, in plant tissues, 160 

in soil, 117, 197, 663-665 
Maturity, 272 

see Winter Injury, Winter Killing. 
Medlar, 400, 555 
Micropyle, 477 
Microsporangium, 473 
Microspore, 478 

Moisture, see Humidity, Soil Moisture, Water. 
Monoecious plants, 490-492 
Mulberry, 404 
Mulching, 34, 307, 315, 334, 353, 368 



N 



Nitrate of soda, see Fertilizers. 
Nitrification, 110-112 
Nitrogen, absorption, 130 

availability, 109-110, 222-224 

deficiencies, 198 

elaboration, 130 

excesses, 195 

fixation, 114-115 

in fertilizers, 123, 201-202, 222-224 



INDEX 



683 



Nitrogen, in plant tissues, 131-138 

relation to fruit-bud formation, 181-185, 
207-208 

relation to fruit coloration, 212 

relation to fruit composition, 215-216 

relation to fruit size, 209-212 

relation to fruit setting, 209, 510 

relation to season of maturity, 216 

relation to vegetative growth, 204-207 

relation to winter injury, 289 

relation to yield, 212-215 

in soil, 113, 222, 663-665 

storage, 135, 138 

translocation, 131-133 
Notching, see Ringing. 
Nubbins, 495 
Nucellus, 477, 483 
Nursery stock, 19, 316, 695-606 

see Stocks. 

O 

(Edema, 84 

Olive, composition, 138, 144, 149, 153, 156, 158, 
159 

fertilizers, 216 

geography, 617 

planting distance, 8 

propagation, 590 

root distribution, 63 

soils, 662, 665 

temperature requirements, 242 

water requirements, 8, 16, 77 
Orange, composition, 138, 144, 149-153, 156, 
158-159 

fertilizers, 216 

fruit setting, 81, 495, 498 

physiological disturbances, 120 

root distribution, 62, 64 

soils, 118 

stocks, 554, 557, 562-563, 572, 575, 580, 587- 
588 

water requirements, 7 

see Citrus Fruits. 
Orchard heating, 373-880 
Osmosis, 20, 105 
Ovary, 473, 475, 487 
Ovule, 476-476 



Papaya, 491, 515 

Parasites and geography of fruit production, 633 

see Diseases. 
Parenchymatosis, 84 
Parthenocarpy, 487, 521-529 
Parthenogenesis, 525 

Pathological conditions, see Physiological Distur- 
bances. 
Peach, composition, 4, 138, 144, 148-150, 156, 287 

cultivation, 289 

fertilizers, 204, 208, 211-212, 215-216, 289 

frost injury, 359-362, 364, 366 

fruit-bud formation, 187 

fruiting habits, 401, 461 

fruit setting, 542 

geography, 620-623, 634 



Peach, irrigation, 71 

propagation, 589 

pruning, 288, 325-326, 410-413, 416, 441, 
461-464 

soils, 657, 665, 670 

stocks, 555, 562, 576, 580, 587, 599 

temperature requirements, 238—240, 245- 
246, 248, 622 

thinning, 290 

varietal and group differences, 285-291, 326, 
362 

water requirements, 3, 6, 16 

whitewashing, 291 

winter injury, 267, 269, 285-292, 298, 312, 
323-326 
Pear, composition, 4, 103-104, 133, 138, 141, 144, 
149, 152-156, 158 

frost injury, 359, 364, 380 

fruit-bud formation, 187, 192 

fruit development, 525, 529, 535 

fruiting habits, 399 

fruit setting, 500, 518, 541, 572 

geography, 248, 612, 614, 619-621 

irrigation, 74 

physiological disturbances, 84, 94, 95 

propagation, 593 

pruning, 408-417, 419-433, 439-447, 450- 
453, 457-461 

soils, 657, 662 

stocks, 312, 553, 557, 566, 570, 572-575, 585, 
588, 601- 602 

varietal and group differences, 323, 430, 541 

water requirements, 3 

winter injury, 312, 322-323 
Pecan, fruiting habits, 405 

fruit setting, 493 

geography, 612, 620-621 

physiological disturbances, 93, 224 

winter injury, 269 
Pedigreed plants, 603-606 
Pentosans, 50, 167, 168-177, 257-260 
Percolation, see Seepage. 
Perennation, 527 
Perisperm, 483 
Persimmon, fruit development, 530, 632-534 

fruiting habits, 404 

fruit setting, 490, 514, 545 

stocks, 559 
Phosphorus, availability, 108, 116, 225 

elaboration, 138 

in fertilizers, 123. 202, 218-219 

in plant tissues, 101-102, 138-144 

in soil, 225, 663-665 

solubility, 225 
Phyllody, 84 
Physiological disturbances , 83-94, 106, 195-197, 

224 
Pigments, 164, 180 
Pinching, 332-333, 453-455, 510 
Pineapple, composition, 150, 153, 158, 159 

fertilizers, 117 

physiological disturbances, 116-117 

soils, 116-117, 658, 662-666 
Pistil abortion, 484, 504, 509, 511 
Placenta, 477 
Planting, depth, 315 



684 



INDEX 



Planting, distances, 8, 59 

season, 19, 269, 316 
Plum, blossoming season, 342 

composition, 4, 102, 103, 132, 133, 138-141, 
144, 149, 150, 153-159 

frost injury, 359, 362 

fruit-bud formation, 187, 192 

fruiting habits, 401 

fruit setting, 484-486, 493, 495, 500, 504, 
505, 511, 642 

geography, 619, 620, 633, 634 

physiological disturbances, 94, 95 

propagation, 589, 590 

pruning, 410, 429, 440, 465 

root distribution, 581 

soils, 668, 669 

stocks, 248, 314, 553, 555, 561, 564, 571, 580, 
581, 584, 586, 588, 602 

temperature requirements, 238, 245 

varietal and group differences, 285, 328, 329, 
362, 495, 542, 669 

water requirements, 3, 8, 16 

whitewashing, 291 

winter injury, 255, 256, 273, 285, 314, 328- 
329 
Polar bodies, 477, 482 
Pollen, abortion, 478, 496-498, 509, 511-512 

carrying agents, 639 

formation, 477-479 

germination, 480-481, 504 

specific effects on fruit, 534-636 
Pollen tube growth, 481, 502, 503, 513, 515 
Pollination, 478, 503, 515, 538-540 
Polyembryony, 504 
Pomegranate, 401, 495, 657 
Potassium, availability, 109 

deficiencies, 106, 198 

displacement, 106 

in fertilizers, 123, 145, 201, 202, 225 

fruit coloration, 145 

in plant tissues, 101, 102, 146-150 

in soil, 145, 663-665 

replacement, 159 
Precipitation, fruit setting, 516, 517 

geography of fruit production, 631-632, 654 

requirements for trees, 6-7 

vegetative growth, 67-70 

winter injury, 266, 270, 274-278 
Propagation, see Grafting, Nursery stock, Stocks. 
Proliferation, 527 
Protandry, 492-494 
Protogyny, 492-494 
Prune, see Plum. 
Pruning, 388-471 

nutritive conditions, 426, 510 

winter-injured trees, 316, 326-326, 432 

winter injury, 288 



Q 



Quince, 150, 187. 400, 542, 657 

R 

Radiation, 338-340, 351, 373-374 
Rainfall, see Precipitation. 
Raphe, 477 



Raspberry, composition, 4, 150, 258 

fertilizers, 207 

fruit-bud formation, 188 

fruiting habits, 402, 467 

fruit setting, 544 

geography, 619 

irrigation, 335 

mulching, 335 

pruning, 332, 333, 453, 467 

soils, 118 

temperature requirements, 628 

varietal and group differences, 332-336 

winter injury, 315, 332-336 
Regularity of bearing, 78, 405 
Respiration, 166 
Rest period, 284-286, 292 
Ringing, 434-437, 506 
Root, distribution, 54-64, 679-588 

killing, 22, 304, 312-316 

pruning, 19, 432-434 
Rosette, 91-92 
Rough bark disease, 85 
Run-off, 7, 32 
Russeting of fruit, 79, 381 



Sap density and hardiness, 264, 257 

Scaly bark disease, 84 

Secondary fertilization, 482 

Second bloom, 191, 381, 415 

Second growth, 70, 270 

Seedlessness, 198, 364, 487, 509, 521-627 

Seeds and fruit development, 629-534 

Seepage, 7, 51, 52 

Selective absorption, 126 

Self fertility, see Fertility. 

Self sterility, see Fertility, Fruitfulness, Fruit 

Setting. 
Setting fruit trees, see Planting. 
Sex distribution, 490-492 
Shadbush, 400 
Shading, 1, 11, 291 

Silicon in plant tissues, 101, 102, 157-168 
Silver leaf, 95 
Sites, 346-351, 653-665 
Slope, 639-643 

Smudging, see Orchard Heating. 
Sodium, 106, 168-159, 663-665 
Sod-mulch, 32-38, 66, 111, 114, 124, 306, 352 

see Soil Management Methods. 
Soil, acidity, see Soil Reaction. 

alkali, see Concentration. 

chemical composition, 662-668 

crop adaptation, 668-671 

fruit setting, 509 

general orchard requirements, 656-658 

management methods, 31-45, 62-64, 111— 
114, 306-307, 352-357 

mechanical analyses, 658-661 

reaction, 116-118, 128, 223, 226, 662 

solubility, 107 

temperature, 247-248, 302-312, 640 

toxins, 122-126 

type and frost danger, 351 

type and frost penetration, 308 



INDEX 



685 



Soil moisture, 47-50 
absorption, 21 
availability, 16, 47-49 
composition, 74 
cover crops, 41-45, 279-281 
disease susceptibility, 75 
evaporation, 282-284 
frost danger, 353-355 
fruit-bud formation, 185 
fruit shape and color, 73 
fruit size, 71 
fruit setting, 616 
intercrops, 39-41 
movement, 51-53 
physiological disturbances, 83-95 
residual effects, 69, 73, 76-78 
root distribution, 60-62 
root killing, 22 
second growth, 70 
soil management methods, 32- 38 
vegetative growth, 22, 34, 66-71 
^ wilting points, 16 

winter injury, 274-284, 309-310 
yield, 34, 72-73, 76-78, 228 
Solubility of soil, 107 
Sour sap, see Sunscald. 
Splitting of fruit, 81 
Spraying in bloom, 519 
Starch, synthesis, 167 

in plant tissues, 169, 173-174 

storage and translocation, 169-170, 173, 

326 
see Carbohydrates. 
Sterility, see Fertility, Fruitfulness, Fruit Setting. 
Stooling, 593 

Stock, influenced by cion, 679-583 
Stock, influence on cion, disease resistance, 568- 
569 
form 560-561 
fruit setting, 510, 572 
fruit size, 572-574 
hardiness, 321, 566-567 
longevity, 578 
maturity, 562-666 
quality, 674-678 
stature, 557-560 
yield, 569-574 
Stocks, congeniality and adaptability, 652-557, 

586-588 
Stocks for, almond, 553, 559, 564, 587, 601 

apple, 553, 554, 558, 559, 562, 56.5-567, 571- 

578, 581, 588-592, 599, 601 
apricot, 556, 575 

cherry, 553, 554, 560, 562, 566, 568, 582, 585 
chestnut, 570 
gooseberry, 553, 568 
grape, 553, 555, 559, 560, 563-565, 567- 

569, 571-578, 580-582, 586-588 
loquat, 553, 564, 575 
medlar, 555 
orange, 554, 557, 562, 563, 567, 572, 575, 

580, 587, 588 
peach, 555, 562, 576, 580, 587, 599 
pear, 553, 557, 566, 570, 572-575, 585, 588, 

601, 602 
persimmon, 559 



Stocks, plum, 553, 555, 561, 562, 564, 571, 574, 
580, 581, 584, 586, 588, 602 

walnut, 568, 588 
Strawberry, composition, 153 

fertilizers, 205, 216, 221 

frost injury, 361-363 

fruit-bud formation, 188, 190 

fruit setting, 487, 490, 495, 498, 510, 513, 544 

irrigation, 75 

mulching, 353 

soils. 118, 662, 666 

varietal and group differences, 362, 363 
Stringfellow root pruning, 19 
Stripping, see Ringing. 
Submergence and root killing, 22 
Sugars, 167-168, 174-179 

see Carbohydrates. 
Sulfur, availability, 109 

deficiencies, 199 

in fertilizers, 151, 202, 219, 226 

in organic compounds, 150 

in plant tissues, 101, 102 

in soil, 151, 663-665 
Summer pruning, 26, 72, 439-453, 463 
Sunscald, 292-296 

Sunshine in fruit growing sections, 633 
Suspensor, 482 
Synergids, 477, 481 



Temperature, 234-235, 621-631 

and assimilation, 165 

and bodies of water, 628-630, 648-650 

critical for flowers, 358-363, 366 

critical for roots, 304, 312-315 

at different elevations, 346-351, 621, 630, 
643-648 

and disease, 248 

and fruit-bud formation, 185 

and fruit setting, 614-516 

heat units and requirements, 236-247, 617- 
630 

inversion, 339, 349-351, 376-378, 646-648 

local variations, 663 

and nitrification, 112 

of plant tissues, 276-278, 293-296, 340, 641 

effects of rapid temperature changes, 260- 
261, 296-300 

sheltered and exposed thermometers, 293, 
340 

of soil, 247-248, 302-312, 640 

influenced by soil and soil management 
methods, 349-356 

and transpiration, 27, 28 
Terminal bud formation, 68—70 
Thermal belts, 646-648 
Thinning and winter injury, 290 
Thinning out, see Pruning. 
Tillage, see Cultivation. 
Tipburn, 87 
Topping, 453 
Toxins, see Soil Toxins. 
Training, 391-396 
Transpiration, 23-28, 126, 449 
Transplanting, see Planting, 



686 INDEX 

Transportation facilities, 639 Water, absorption, see Absorption. 

Trunk splitting, 298-300 adsorption, see Adsorption. 

Tufting of carpels and seeds, 84 conduction, 28-29, 276 

Watercore, 85 
U Water content, plant tissues, 4-5, 50, 275, 276, 

287, 294, 319, 320 
Unfruitfulness, see Fruitfulness. soi^ 13-17, 49 

Water, requirements, 1-13 

V retention, 255-260, 274-276 

Whitewashing, 291, 296, 368 
Variegation, 569 _ ^ wilting coefficient) 13 _ 17 

Wind, influence on, evaporation, 45, 281-281, 634 



Verdant zones, 646-648 



Virescence, 85 



frost, 341, 378, 379 
fruit setting, 518 
transpiration, 26-27 



Walnut, composition, 4, 138, 144, 149, 152-159 winter injury, 273 

fruiting habits, 405 Windbreaks, 46, 81, 281-284, 652 

fruit setting, 493 Winter killing, 260-262, 296-300, 566-567 

geography, 620 Winter injury, 264-278, 292-336, 651 

physiological disturbances, 88 

stocks, 568, 588 X 

water requirements, 3, 16 

winter injury, 268 Xenia, 482 



